Precise Capture and Direct Quantification of Tumor Exosomes via a Highly Efficient Dual-Aptamer Recognition-Assisted Ratiometric Immobilization-Free Electrochemical Strategy

Bilateral efforts to improve SERS detection efficiency of exosomes by Au/Na7PMo11O39 Combined with Phospholipid Epitope Imprinting

Detection of cancer-related exosomes in body fluids has become a revolutionary strategy for early cancer diagnosis and prognosis prediction. We have developed a two-step targeting detection method, termed PS-MIPs-NELISA SERS, for rapid and highly sensitive exosomes detection. In the first step, a phospholipid polar site imprinting strategy was employed using magnetic PS-MIPs (phospholipids-molecularly imprinted polymers) to selectively isolate and enrich all exosomes from urine samples. In the second step, a nanozyme-linked immunosorbent assay (NELISA) technique was utilized. We constructed Au/Na7PMo11O39 nanoparticles (NPs) with both surface-enhanced Raman scattering (SERS) property and peroxidase catalytic activity, followed by the immobilization of CD9 antibodies on the surface of Au/Na7PMo11O39 NPs. The Au/Na7PMo11O39-CD9 antibody complexes were then used to recognize CD9 proteins on the surface of exosomes enriched by magnetic PS-MIPs. Lastly, the high sensitivity detection of exosomes was achieved indirectly via the SERS activity and peroxidase-like activity of Au/Na7PMo11O39 NPs. The quantity of exosomes in urine samples from pancreatic cancer patients obtained by the PS-MIPs-NELISA SERS technique showed a linear relationship with the SERS intensity in the range of 6.21 × 107-2.81 × 108 particles/mL, with a limit of detection (LOD) of 5.82 × 107 particles/mL. The SERS signal intensity of exosomes in urine samples from pancreatic cancer patients was higher than that of healthy volunteers. This bidirectional MIPs-NELISA-SERS approach enables noninvasive, highly sensitive, and rapid detection of cancer, facilitating the monitoring of disease progression during treatment and opening up a new avenue for rapid early cancer screening.

Target proteins-regulated DNA nanomachine-electroactive substance complexes enable separation-free electrochemical detection of clinical exosome

Simple and reliable profiling of tumor-derived exosomes (TDEs) holds significant promise for the early detection of cancer. Nonetheless, this remains challenging owing to the substantial heterogeneity and low concentration of TDEs. Herein, we devised an accurate and highly sensitive electrochemical sensing strategy for TDEs via simultaneously targeting exosomal mucin 1 (MUC1) and programmed cell death ligand 1 (PD-L1). This approach employs high-affinity aptamers as specific recognition elements, utilizes rolling circle amplification and DNA nanospheres as effective bridges and signal amplifiers, and leverages methylene blue (MB) and doxorubicin (DOX) as robust signal reporters. The crux of this separation- and label-free method is the specific response of MB and DOX to G-quadruplex structures and DNA nanospheres, respectively. Quantifying TDEs using this strategy enabled precise discrimination of lung cancer patients (n = 25) from healthy donors (n = 12), showing 100% specificity (12/12), 92% sensitivity (23/25), and an overall accuracy of 94.6% (35/37), with an area under the receiver operating characteristic curve (AUC) of 0.97. Furthermore, the assay results strongly correlated with findings from computerized tomography and pathological analyses. Our approach could facilitate the early diagnosis of lung cancer through TDEs-based liquid biopsy.

Boronate crosslinking-based ratiometric electrochemical assay of glycated albumin

As a product of nonenzymatic glycation, glycated albumin (GA) is a promising serum marker for the short-term glycemic monitoring in patients with diabetes. On the basis of the boronate crosslinking (BCL)-enabled direct labeling of ferrocene (Fc) tags to the nonenzymatically glycated (NEG) sites, we report herein a novel aptamer-based ratiometric electrochemical (apt-REC) platform for the point-of-care (POC) assay of GA. This apt-REC platform is based on the recognition of GA proteins by the methylene blue (MB)-modified aptamer receptors and the labeling of the Fc tags to the NEG sites via the BCL. Using MB as the reference tag and Fc as the quantification tag, the ratio of the oxidation currents (i.e., IFc/IMB) can serve as the yardstick for the ratiometric assay of GA. Due to the presence of tens of the NEG sites, each GA protein can be labeled with tens of quantification tags, permitting the amplified assay in a simple, time-saving, and low-cost manner. The ratiometric signal exhibited a good linear response over the range from 0.1 to 100 μg/mL, with a detection limit of 45.5 ng/mL. In addition to the superior reproducibility and robustness, this apt-REC platform is highly selective (capable of discriminating GA against human serum albumin (HSA)) and applicable to GA assay in serum samples. Due to its low cost, high reproducibility and robustness, simple operation, and high sensitivity and selectivity, this apt-REC platform holds great promise in the POC assay of GA for diabetes management.

Label-Free and DNAzyme-Mediated Biosensor with a High Signal-to-Noise Ratio for a Lumpy Skin Disease Virus Assay

Lumpy skin disease virus (LSDV) is a severe and highly contagious form of cowpox. As LSDV continues to mutate and there is no vaccine and treatment in nonendemic countries, early detection of LSDV becomes an important basis for epidemic prevention and control, especially for detection of conserved sequences. A new label-free and sensitive fluorescence method was developed based on a light-up RNA aptamer for detecting LSDV. The method integrated recombinase polymerase amplification (RPA), CRISPR/Cas12a, 10-23 DNAzyme, and Baby Spinach RNA aptamer for triple cascade signal amplification. Based on highly sensitive and specific RPA and CRISPR/Cas12a, DNAzyme achieved a third signal amplification. Additionally, the Baby Spinach RNA aptamer had stronger fluorescence signals and higher quantum yields. The label-free method had ultrahigh sensitivity with the actual detection limit as 1.29 copies·μL-1. The method was 100-fold more sensitive compared to RPA with Cas12a. Moreover, it had no cross-reactivity with viruses belonging to the Capripoxvirus, such as sheep pox virus and goat pox virus with genetic homology as 97%. Furthermore, the method displayed 100% accuracy in 50 actual samples. Therefore, the method based on RPA, Cas12a, and 10-23 DNAzyme had advantages in LSDV detection and provided a new solution for LSD prevention and control.

Pushing Forward the DNA Walkers in Connection with Tumor-Derived Extracellular Vesicles

Extracellular vesicles (EVs) are microparticles released from cells in both physiological and pathological conditions and could be used to monitor the progression of various pathological states, including neoplastic diseases. In various EVs, tumor-derived extracellular vesicles (TEVs) are secreted by different tumor cells and are abundant in many molecular components, such as proteins, nucleic acids, lipids, and carbohydrates. TEVs play a crucial role in forming and advancing various cancer processes. Therefore, TEVs are regarded as promising biomarkers for the early detection of cancer in liquid biopsy. However, the currently developed TEV detection methods still face several key scientific problems that need to be solved, such as low sensitivity, poor specificity, and poor accuracy. To overcome these limitations, DNA walkers have emerged as one of the most popular nanodevices that exhibit better signal amplification capability and enable highly sensitive and specific detection of the analytes. Due to their unique properties of high directionality, flexibility, and efficiency, DNA walkers hold great potential for detecting TEVs. This paper provides an introduction to EVs and DNA walker, additionally, it summarizes recent advances in DNA walker-based detection of TEVs (2018-2024). The review highlights the close relationship between TEVs and DNA walkers, aims to offer valuable insights into TEV detection and to inspire the development of reliable, efficient, simple, and innovative methods for detecting TEVs based on DNA walker in the future.

Platinum single atom on CsPbBr3 nanocrystals as electrocatalyst boosts electrochemical sensing of ascorbic acid

Monitoring ascorbic acid (AA) levels in human body can provide valuable clues for disease diagnosis. Anchoring noble metal single atoms on perovskite substrate is a promising strategy to design electrocatalysts with outstanding electrocatalytic performance. Herein, we design an electrochemical method for detecting AA by utilizing Pt single atoms-doped CsPbBr3 nanocrystals (Pt SA/CsPbBr3 NCs) fixed on a glassy carbon electrode as an electrochemical catalyst. The uncharged 3,5,3',5'-tetramethylbenzidine (TMB) undergoes oxidation to form the positively charged oxidized TMB (oxTMB) owing to the exceptional electrochemical catalytic performance of Pt SA/CsPbBr3 NCs. Subsequently, the target AA reduces oxTMB to TMB, which is then electrocatalytically oxidized to oxTMB, producing significant oxidation current. In this way, such characteristic provides a sensitive electrochemical strategy for AA detection, achieving a concentration range of 50-fold with the detection limit of 0.0369 μM. The developed electrochemical method also successfully generates accurate detection response of AA in complex sample media (urine). Overall, this approach is expected to offer a novel way for early disease diagnosis.

Electrochemiluminescence biosensor for specific detection of pancreatic ductal carcinoma through dual targeting of MUC1 and miRNA-196a

Pancreatic ductal adenocarcinoma (PDAC) poses significant diagnostic challenges due to its asymptomatic nature in its early stages, low specificity of conventional in vitro assays, and limited efficacy of surgical interventions. However, clinical specificity of the current serum biomarkers is suboptimal, leading to diagnostic inaccuracies and oversights. Therefore, this study introduced a novel dual-target electrochemiluminescence (ECL) biosensor to address these critical issues. The ECL biosensor synergistically employs the serum biomarker MUC1 and microRNA-196a to detect early-stage PDAC precisely. While MUC1 is a differential marker between normal and cancerous pancreatic cells, its standalone diagnostic performance is limited. However, integrating miRNA-196a as a complementary marker substantially enhances the specificity of the assay. This biosensor exhibits distinct ECL signal modulation-"on-off" in the presence of MUC1 and "off-on" upon concurrent detection of MUC1 and miRNA-196a. The biosensor achieves remarkably low limits of detection (LODs) at 0.63 fg mL-1 and 4.57 aM for MUC1 and miRNA-196a, respectively. Thus, it facilitates the real-time differentiation between human normal pancreatic (hTERT-HPNE) and pancreatic cancer (PANC-1) cells in authentic biological matrices. This innovative approach heralds a significant advancement in the early and specific detection of PDAC, offering promising prospects for clinical translation and the broader landscape of cancer diagnostics.

A highly sensitive Lock-Cas12a biosensor for detection and imaging of miRNA-21 in breast cancer cells

The expression levels of microRNA (miRNA) vary significantly in correlation with the occurrence and progression of cancer, making them valuable biomarkers for cancer diagnosis. However, their quantitative detection faces challenges due to the high sequence homology, low abundance and small size. In this work, we established a strand displacement amplification (SDA) approach based on miRNA-triggered structural "Lock" nucleic acid ("Lock" DNA), coupled with the CRISPR/Cas12a system, for detecting miRNA-21 in breast cancer cells. The "Lock" DNA freed the CRISPR-derived RNA (crRNA) from the dependence on the target sequence and greatly facilitated the extended detection of different miRNAs. Moreover, the CRISPR/Cas12a system provided excellent amplification ability and specificity. The designed biosensor achieved high sensitivity detection of miRNA-21 with a limit of detection (LOD) of 28.8 aM. In particular, the biosensor could distinguish breast cancer cells from other cancer cells through intracellular imaging. With its straightforward sequence design and ease of use, the Lock-Cas12a biosensor offers significant advantages for cell imaging and early clinical diagnosis.

Exo Ⅲ-assisted amplification signal strategy synergized with Au@Pt NFs/CoSe2 for sensitive detection of enrofloxacin

Overuse of enrofloxacin (ENR) has posed a potential threat to ecosystems and public health, so it is critical to sensitive and accurate determination of ENR residues. In this work, a novel ultra-sensitive and specific electrochemical aptasensor was fabricated based on the cobalt diselenide loaded gold and platinum nanoflowers (Au@Pt NFs/ CoSe2) and Exonuclease III (Exo III)-assisted cycle amplification strategy for the detection of ENR. Au@Pt NFs/ CoSe2 nanosheets as the substrate material, with large surface area, accelerate electron transfer and attach more DNA probes on the electrode substrate, have effectively enhanced the electrochemical performance of the electrode. With the existence of Enrofloxacin (ENR), the aptamer recognizes and binds to ENR, thus the signal probe cDNA was released and immobilized onto the electrode surface to hybridized with methylene blue (MB) labelled DNA (MB-DNA), thereby triggering the Exo III-assisted cycle for further signal amplification. As expected, the prepared aptasensor demonstrated excellent sensitivity and selectivity, with a wide linear range from 5.0 × 10-6 ng/mL to 1.0 × 10-2 ng/mL for ENR, a low detection limit of 1.59 × 10-6 ng/mL. Consequently, this strategy provided a promising avenue for ultrasensitive and accurate detection of ENR in milk samples.

Visually evaluating drug efficacy in living cells using COF-based fluorescent nanoprobe via CHA amplified detection of miRNA and simultaneous apoptosis imaging

BACKGROUNDS

Cancer is a highly fatal disease which is close relative of miRNA aberrant expression and apoptosis disorders. Elucidation of the therapeutic efficacy through investigating the changes in miRNA and apoptosis holds immense importance in advancing the development of miRNA-based precision therapy. However, it remains a challenge as how to visually evaluate the efficacy during protocol optimization of miRNA-based anticancer drugs at the cellular level. Therefore, exploring effective and noninvasive methods for real-time monitoring of therapeutic efficacy in living cells is of great significance.

RESULTS

Herein, we reported a novel fluorescent nanoprobe COF-H1/H2-Peptide for visually evaluating drug efficacy in living cells through amplified imaging of low-abundant miRNA-221 with catalytic hairpin assembly (CHA) circle amplification, as well as simultaneous caspase-3 imaging. With strong stability and good biocompatibility, this newly fabricated amplified nanoprobe showed high sensitivity and specificity for the detection of miRNA-221 and caspase-3, and the limit of detection (LOD) of miRNA-221 was as low as 2.79 pM. The fluorescent imaging results showed that this amplified nanoprobe could not only detect caspase-3 in living cells, but also effectively detect low levels of miRNA-221 with increasing anticancer drug concentration and treatment time. The smart nanoprobe had effective performance for optimizing miRNA-based drug treatment schedules by dual-color fluorescence imaging.

SIGNIFICANCE

This nanoprobe combined CHA amplified detection of intracellular miRNA-221 and synchronous apoptosis imaging, with excellent sensitivity for the detection of cellular low-level miRNA, enabling the realization of real-time assessment of the efficacy of miRNA-based therapy in living cells. This work presents a promising approach for revealing the regulatory mechanisms between miRNAs and apoptosis in cancer occurrence, development, and treatment.

One-step and label-free ratiometric fluorescence assay for the detection of plasma exosome towards cancer diagnosis

Exosomes are closely associated with tumor development and are regarded as viable biomarkers for cancer. Here, a ratiometric fluorescence method was proposed for the one-step and label-free detection of plasma exosomes. A bicolor streptavidin magnetic beads were specifically created with an immobilized Cy5-labeled hairpin aptamer for CD63 (Cy5-Apt) on its surface to identify exosome, and a green color SYBR Green I (SGI) embedded in the stem of Cy5-Apt to respond to exosomes. After exosome capture, the Cy5-Apt could undergo a conformational shift and release the encapsulated SGI, allowing exosome measurement based on the fluorescence ratio of Cy5 and SGI. The enrichment, separation and detection of exosomes in proposed method could be completed in one step (30 min), which is a significant improvement over previous method. Furthermore, the use of ratiometric fluorescence and magnetic separation allows for exosome enrichment and interference elimination from complex matrices, improving accuracy and sensitivity. Particularly, the assay could detect exosomes in plasma and has potential to distinguish lung cancer patients from healthy volunteers with an area under the receiver operator characteristic curve of 0.85. Besides, the study provided an efficient method for analyzing the various divisions of exosomes by merely modifying the aptamer, which holds great promise for point-of-care applications.

Selective Extraction and Quantification of Hemoglobin Based on a Novel Molecularly Imprinted Nanopolymeric Structure of Poly(acrylamide-vinyl imidazole)

Imbalances in hemoglobin (Hb) levels can lead to conditions such as anemia or polycythemia, emphasizing the importance of precise Hb extraction from blood. To address this, a novel synthetic imprinted polymer was meticulously developed for capturing and separating Hb. Poly(acrylamide-vinylimidazole) nanopolymer (poly(AAm-VIM)) was synthesized using acrylamide and vinyl imidazole as functional monomers through surfactant-free emulsion polymerization. Characterization using FTIR, particle size, zeta potential, and SEM ensured the polymer's structure. The Hb-imprinted nanopolymer (Hb-poly(AAm-VIM)) demonstrated notable specificity, with a calculated Hb-specific adsorption value (Qmax) of 3.7377 mg/g in a medium containing 2.5 mg/mL Hb. The molecularly imprinted polymer (MIP) exhibited approximately 5 times higher Hb adsorption than the nonimprinted polymer (NIP). Under the same conditions, the imprinted nanopolymer displayed 2.39 and 2.17 times greater selectivity for Hb over competing proteins such as bovine serum albumin (BSA) and lysozyme (Lys), respectively. Also, SDS-PAGE analysis results confirmed the purification of Hb by the molecularly imprinted nanopolymer. These results underscore the heightened specificity and efficacy of the molecularly imprinted nanopolymer in selectively targeting Hb atoms among other proteins. Incorporating such polymers is justified by their notable affinity, cost-effectiveness, and facile production. This research contributes valuable insights into optimizing synthetic imprinted polymers for efficient Hb extraction, with potential in medical diagnostics and treatment applications.

Colorimetric and fluorescent independent dual "signal on" biosensor for accurate detection of ochratoxin A based on aptamer-triggered biocatalytic reactions

Ochratoxin A (OTA) is a hazardous food contaminant with significant health risks. Dual-channel OTA detection is noted for its cross-reference capability and high accuracy. Still, challenges in addressing in-system corrections and "signal off" related false positives and limited signal gains remain. Herein, we developed a dual-channel "signal on" aptasensor with one recognition process and two independent signal outputs for OTA analysis. The OTA aptamer binds to magnetic beads (MBs) and partially hybridizes with a complementary-trigger (cDNA-Trigger) sequence. Adding OTA disrupts the duplex sequence, leading to G-quadruplex (G4) formation and enrichment on the MBs, which then interacts with hemin to catalyze a color signal. Concurrently, the freed cDNA-Trigger catalyzes an enzyme-free DNA circuit, producing a fluorescence signal. The magnetic enrichment and signal amplification strategies make the proposed assay demonstrate excellent sensitivity toward OTA, with limits of detection (LOD) of 0.017 pM in the fluorescence channel and 48.1 pM in the colorimetric channel. Both channels have effectively detected OTA in grape juice and baijiu, demonstrating their applicability and reliability. Moreover, given the widespread use of smartphones globally, a mini-program with a self-correction function was designed to facilitate on-site colorimetric channel monitoring, making OTA detection more accessible and user-friendly.

Light-harvesting iridium (III) complex-sensitized NiO photocathode for photoelectrochemical bioanalysis

A novel iridium (III) complex bearing boron dipyrromethene (Bodipy) as the light-harvesting antenna has been synthesized and is firstly employed as photosensitizer to assemble a dye-sensitized NiO photocathode. The assembled photocathode exhibits significantly improved photoelectrochemical (PEC) performance. Integrating the prepared photocathode with hybridization chain reaction (HCR)--based signal amplification strategy, a cathodic PEC biosensor is proposed for the detection of microRNA-133a (miRNA-133a). In the presence of the target, HCR is triggered to form long duplex concatamers on the photocathode, which allows numerous manganese porphyrins (MnPP) to bind in the dsDNA groove. With the help of H2O2, MnPP with peroxidase-like activity catalyzes 4--chloro-1-naphthol (4-CN) to produce benzo--4--chlorohexadienone (4-CD) precipitate on the electrode, leading to a significant decrease of photocurrent signal. The decreased photocurrent correlates linearly with the target concentration from 0.1 fM to 1 nM with a detection limit of 66.2 aM (S/N = 3). The proposed PEC strategy exhibits delightful selectivity, reproducibility and stability.

Magnetically-assisted electrochemical immunoplatform for simultaneous detection of active and total prostate-specific antigen based on proteolytic reaction and sandwich affinity analysis

Simultaneous detection of active and inactive proteases is clinically meaningful for improving diagnostic specificity. In this work, we reported an electrochemical method for simultaneous immunoassays of active and total proteases. Magnetic beads (MBs) were used as the solid supports for immobilization of capture antibodies and enrichment of targets. For the detection of active protease, the proteolytic-reaction-based analysis was carried out by the generation of Cu2+-binding peptide, in which a label-free peptide was used as the proteolytic substrate. The redox potential of the resulting peptide-Cu2+ complex was intrinsically distinguished from that of free Cu2+, thus allowing the "signal-on" detection of active protease. For the immunoassay of total protease in a sandwich-like format, electroactive metal-organic frameworks (Cu-MOFs) were used as the signal tags. The captured Cu-MOFs could directly produce a well-defined electrochemical signal from the reduction of Cu2+ ions. The analytical performances of the immunoplatform were evaluated by determining the model analytes of free and total prostate-specific antigen (fPSA and tPSA) in buffer and serum. The detection limits were found to be 0.3 pM for fPSA and 2 pM for tPSA. This work proposed a new strategy for simultaneous detection of active and total proteases, which should be evaluable for clinical diagnosis and treatment of protease-relative diseases.

Nanozyme-Enhanced Electrochemical Biosensors: Mechanisms and Applications

Nanozymes, as innovative materials, have demonstrated remarkable potential in the field of electrochemical biosensors. This article provides an overview of the mechanisms and extensive practical applications of nanozymes in electrochemical biosensors. First, the definition and characteristics of nanozymes are introduced, emphasizing their significant role in constructing efficient sensors. Subsequently, several common categories of nanozyme materials are delved into, including metal-based, carbon-based, metal-organic framework, and layered double hydroxide nanostructures, discussing their applications in electrochemical biosensors. Regarding their mechanisms, two key roles of nanozymes are particularly focused in electrochemical biosensors: selective enhancement and signal amplification, which crucially support the enhancement of sensor performance. In terms of practical applications, the widespread use of nanozyme-based electrochemical biosensors are showcased in various domains. From detecting biomolecules, pollutants, nucleic acids, proteins, to cells, providing robust means for high-sensitivity detection. Furthermore, insights into the future development of nanozyme-based electrochemical biosensors is provided, encompassing improvements and optimizations of nanozyme materials, innovative sensor design and integration, and the expansion of application fields through interdisciplinary collaboration. In conclusion, this article systematically presents the mechanisms and applications of nanozymes in electrochemical biosensors, offering valuable references and prospects for research and development in this field.

Thermophoretic Aggregation Imaging of Tumor-Derived Exosomes by CRISPR-Cas13a-Based Nanoprobes

The inherent heterogeneity of tumor-derived exosomes holds great promise for enhancing the precision of cancer diagnostics. MicroRNAs (miRNAs) encapsulated in tumor-associated exosomes have emerged as valuable biomarkers for the early detection of cancers. Nevertheless, the flexible structure and inherent instability of RNA limit its application in biological diagnostics. The CRISPR-Cas13a system, distinguished by its target-responsive "collateral effect", represents a powerful tool for advancing cancer diagnostics. In this study, we harness the CRISPR-Cas13a system as an innovative signal amplification tool to image cancer-related exosomal miRNA in situ. Furthermore, we capitalize on the thermophoretic aggregation effect exhibited by gold nanoparticles (Au NPs) to consolidate the fluorescent signals generated by the CRISPR-Cas13a system. Subsequently, the developed nanoprobe is applied to detect lung cancer-related exosomal miRNA from human serum, enabling the aggregated visualization of low-abundance cancer exosomes in individuals with lung cancer compared with healthy individuals. This sensitive thermophoretic aggregation assay provides a diagnostic tool for lung cancer in the clinic.

Paper-based electrochemical device for early detection of integrin αvβ6 expressing tumors

Despite progress in the prevention and diagnosis of cancer, current technologies for tumor detection present several limitations including invasiveness, toxicity, inaccuracy, lengthy testing duration and high cost. Therefore, innovative diagnostic techniques that integrate knowledge from biology, oncology, medicinal and analytical chemistry are now quickly emerging in the attempt to address these issues. Following this approach, here we developed a paper-based electrochemical device for detecting cancer-derived Small Extracellular Vesicles (S-EVs) in fluids. S-EVs were obtained from cancer cell lines known to express, at a different level, the αvβ6 integrin receptor, a well-established hallmark of numerous epithelial cancer types. The resulting biosensor turned out to recognize αvβ6-containing S-EVs down to a limit of 0.7*103 S-EVs/mL with a linear range up to 105 S-EVs /mL, and a relative standard deviation of 11%, thus it may represent a novel opportunity for αvβ6 expressing cancers detection.

Simultaneous Electrochemical Detection of Multiple Bacterial Species Using Metal-Organic Nanohybrids

Organic metallic nanohybrids (NHs), in which many small metal nanoparticles are encapsulated within a conductive polymer matrix, are useful as sensitive electrochemical labels because the constituents produce characteristic oxidation current responses. Gold NHs, consisting of gold nanoparticles and poly(m-toluidine), and copper NHs, consisting of copper nanoparticles and polyaniline, did not interfere with each other in terms of the electrochemical signals obtained on the same electrode. Antibodies were introduced into these NHs to function as electrochemical labels for targeting specific bacteria. Electrochemical measurements using screen-printed electrodes dry-fixed with NH-labeled bacterial cells enabled the estimation of bacterial species and number within minutes, based on the distinct current response of the labels. Our proposed method achieved simultaneous detection of enterohemorrhagic Escherichia coli and Staphylococcus aureus in a real sample. These NHs will be powerful tools as electrochemical labels and are expected to be useful for rapid testing in food and drug-related manufacturing sites.

Electrochemical detection of glutathione based on accelerated CRISPR/Cas12a trans-cleavage with MnO2 nanosheets

The CRISPR/Cas12a system is accelerated by glutathione-mediated reduction of MnO2 nanosheets. By monitoring the trans-cleavage of the DNA probe, an electrochemical method for glutathione assay is fabricated, with the detection limit of 3.5 pM. It provides a promising tool for plasma analysis with satisfactory performance, indicating the broad application prospects of this glutathione assay.

A novel nanoprobe for visually investigating the controversial role of miRNA-34a as an oncogene or tumor suppressor in cancer cells

MiRNA-targeted therapy has become a hot topic in current cancer research. The key to this treatment strategy is to clarify the specific role of miRNA in cancer. However, the roles of some miRNAs acting as oncogenic or tumor suppressors are still controversial, which are influenced by different tumor types, even in the same cancer type. Hence, we designed a novel fluorescent nanoprobe based on polydopamine nanoparticles (PDA NPs) for simultaneously detecting caspase-3 and miRNA-34a within living cells. The specific role of miRNA-34a in different cancer cells could be further identified by studying the expression alterations of caspase-3 and miRNA-34a. Confocal imaging indicated that miRNA-34a indeed acted as a tumor suppressor in anticancer drug-treated MCF-7 and HeLa cells, where the effect of miRNA-34a remains controversial. The designed nanoprobe can offer a promising approach to ascertain the oncogenic or tumor-suppressing role of miRNA in different cancer cells with a simple visualization method, which has valuable implications for exploring the practicability of precision therapy focused on miRNA and evaluating the efficacy of new miRNA-targeted anticancer medications.

Highly reproducible electrochemical biosensor for Influenza A virus towards low-resource settings

A highly reproducible electrochemical biosensor, employing a five-stranded four-way junction (5S-4WJ) system through square wave voltammetry, has been successfully validated for the detection of Influenza A virus (InfA). A comprehensive assessment of its linearity, precision, accuracy, and robustness has demonstrated its compliance with FDA standards. Integration with Nucleic Acid-Based Amplification (NASBA) has showcased its selectivity for InfA, enabling the detection of InfA RNA with a standard heater set at 41 °C. This platform offers a straightforward setup well-suited for use at low-resource facilities.

Immunomagnetic capture and traceless release of native tumor-derived exosomes from human plasma for exploring interaction with recipient cells by aptamer-functionalized nanoflowers

BACKGROUND

Tumor-derived exosomes (TEXs) play an important role in the development process of cancer, which can transport a large number of carcinogenic molecules to normal cells, and subsequently promote tumor metastasis. However, TEXs that were utilized in most of previous researches were obtained from the cell medium of tumor cell lines, which cannot reflect the physiological state of primary cells in vivo. Isolation of native TEXs from human plasma with intact function is contributed to exploring the interaction between TEXs and recipient cells for understanding their true biological functions.

RESULTS

We developed a strategy that involves both capture and release processes to obtain native TEXs from plasma of cancer patients. An MoS2-based immunomagnetic probe (Fe3O4@MoS2-Au-Aptamer, named as FMAA) with the advantages of high surface area, magnetic response and abundant affinity sites was designed and synthesized to capture TEXs through recognizing high-expression tumor-associated antigens of EpCAM. With the assistance of complementary sequences of EpCAM, TEXs were released with non-destruction and no residual labels. According to NTA analysis, 107-108 TEXs were recovered from per mL plasma of breast cancer patients. The interaction between native TEXs and normal epithelial cells confirms TEXs could induce significant activation of autophagy of recipient cells with co-culture for 12 h. Proteomics analysis demonstrated a total of 637 proteins inside epithelial cells had dynamic expression with the stimulation of TEXs and 5 proteins in the pathway of autophagy had elevated expression level.

SIGNIFICANCE

This work not only obtains native TEXs from human plasma with non-destruction and no residual labels, but also explores the interaction between TEXs and recipient cells for understanding their true biological functions, which will accelerate the application of TEXs in the field of biomarkers and therapeutic drugs.

A "signal-off" electrochemiluminescence immunosensor based on electron transfer between core-shell emitter Ag@SiO2 and quencher CeO2

Silver nanoparticles (Ag·NPs) show promising advantages in electrochemiluminescence (ECL) owing to their favorable optical properties and biocompatibility. However, their susceptibility to oxidation and degradation in the presence of air adversely affects ECL intensity. In this study, we employed a sandwich sensing platform using silica-coated silver nanoparticles (Ag@SiO2) as a novel luminescent material and cerium dioxide (CeO2) as an ECL signal quencher for sensitive neuro-specific enolase (NSE) detection. The core-shell structure protected Ag NPs within the silica (SiO2) layer, enhancing their ECL luminescence properties by reducing external environmental influence and preventing Ag NPs aggregation. Amino-functionalized CeO2 efficiently diminished Ag@SiO2 ECL emission through electron transfer, resulting in a "signal-off" detection mode with high sensitivity and accuracy. The detection limit reached 1.66 fg/mL, and the detection range spanned from 100 fg/mL to 500 ng/mL, showcasing a powerful biomolecule detection strategy.

Glowing Octopus-Inspired Nanomachine: A Versatile Aptasensor for Efficient Capture, Imaging, Separation, and NIR-Triggered Release of Cancer Cells

The separation and analysis of circulating tumor cells (CTCs) in liquid biopsy significantly facilitated clinical cancer diagnosis and personalized therapy. However, current methods face challenges in simultaneous efficient capturing, separation, and imaging of CTCs, and most of the devices cannot be reused/regenerated. We present here an innovative glowing octopus-inspired nanomachine (GOIN), capable of capturing, imaging, separating, and controlling the release of cancer cells from whole blood and normal cells. The GOIN comprises an aptamer-decorated magnetic fluorescent covalent organic framework (COF), which exhibits a strong affinity for nucleolin-overexpressed cancer cells through a multivalent binding effect. The captured cancer cells can be directly imaged using the intrinsic stable fluorescence of the COF layer in the GOIN. Employing magnet and NIR laser assistance enables easy separation and mild photothermal release of CTCs from the normal cells and the nanomachine without compromising cell viability. Moreover, the GOIN demonstrates a reusing capability, as the NIR-triggered CTC release is mild and nondestructive, allowing the GOIN to be reused at least three times.

Split aptamer-based sandwich-type ratiometric biosensor for dual-modal photoelectrochemical and electrochemical detection of 17β-estradiol

BACKGROUND

As one of the most potent environmental estrogens, 17β-estradiol (E2), which can be enriched into organisms through the food chain and cause harmful biological effects in humans, has been frequently detected in the water environment of the world. High performance liquid chromatography (HPLC) and gas chromatograohy-mass spectrometry (GC/MS) have been widely used for quantification of E2. Despite excellent accuracy, tedious pretreatment and expensive instruments result in their limited application. It is clear that there is an urgent need to establish simple, sensitive and accurate methods for the determination of E2.

RESULTS

A split aptamer-based sandwich-type ratiometric biosensor based on split aptamer was developed by coupling photoelectrochemical and electrochemical assays for E2 detection. For analysis, the two fragments of split aptamer recognized E2 by forming sandwich structure, which triggered hybridization chain reaction (HCR) to produce double-stranded DNA (dsDNA) with CdTe quantum dots (QDs) labeled hairpin DNA. The resultant dsDNA can further absorb methylene blue (MB) to sensitize CdTe QDs for an enlarged photocurrent (IPEC) and output a redox current of IMB, and both of them acted as response signals for detection; [Fe(CN)6]3-/4- probe produced redox current of I[Fe(CN)6]3-/4- as reference signal. Using IMB/I[Fe(CN)6]3-/4- and IPEC/I[Fe(CN)6]3-/4- as yardsticks, the developed split aptamer-based sandwich-type ratiometric biosensor provides two linear ranges of 0.1-5000 pg mL-1 for IMB/I[Fe(CN)6]3-/4- and 0.1-10000 pg mL-1 for IPEC/I[Fe(CN)6]3-/4- with detection limits of 0.06 pg mL-1 and 0.02 pg mL-1, respectively.

SIGNIFICANCE

These results of the biosensor are benefiting from the coupling of photoelectrochemical (PEC) and electrochemical (EC) assays as well as the unique cooperative recognition mechanism of split aptamer. This method not only enabled the biosensor to be successfully applied to the determination of E2 in lake water, but also broadens the prospects for the realization of sensitive and accurate detection of E2.

Immobilization-free dual-aptamer-based photoelectrochemical platform for ultrasensitive exosome assay

Exosomes, involved in cancer-specific biological processes, are promising noninvasive biomarkers for early diagnosis of cancer. Herein, an immobilization-free dual-aptamer-based photoelectrochemical (PEC) biosensor was proposed for the enrichment and quantification of cancer exosome based on photoactive bismuch oxyiodide/gold/cadmium sulfide (BiOI/Au/CdS) composites, nucleic acid-based recognition and signal amplification. In this biosensor, the recognition of exosome by two aptamers would trigger the deoxyribonucleotidyl transferase (TdT) enzyme-aided polymerization, leading to the enrichment of alkaline phosphatase (ALP) on Fe3O4 surface. After magnetic separation, ALP could catalyze the generation of ascorbic acid (AA) as electron donor and initiate the following redox cycle reaction for further signal amplification. Furthermore, all the above processes were performed in solution, the recognition and signal amplification efficiency would be superior than the heterogeneous strategy owing to the avoidance of steric hindrance effect. As a result, the proposed PEC biosensor was capable of enriching and detecting of cancer exosomes with high sensitivity and selectivity. The linear range of the biosensor was from 1.0 × 102 particles·μL-1 to 1.0 × 106 particles·μL-1 and the detection limit was estimated to be 21 particles·μL-1. Therefore, the proposed PEC biosensor holds great promise in quantifying tumor exosome for nondestructive early clinical cancer diagnosis and various other bioassay applications.

Multivalent DNA Flowers for High-Performance Isolation, Detection, and Release of Tumor-Derived Extracellular Vesicles

Tumor-derived extracellular vesicles (T-EVs) hold great promise for understanding cancer biology and improving cancer diagnostics and therapeutics. Herein, we developed multivalent DNA flowers (DFs) containing repeated and equidistant EpCAM aptamers for the efficient isolation of T-EVs. The multivalent aptamer chains in DFs had good flexibility to adapt to the surface morphology of T-EVs and achieved multivalent ligand-receptor interactions, thus showing enhanced isolation ability compared to monovalent aptamers. Compared with other materials for isolation of EVs, DFs were generated by rolling circle amplification (RCA) and self-assembled into microspheres in a one-pot reaction, and the recognition molecules (aptamers) were directly replicated and assembled during the RCA reaction instead of chemical modification and immobilization on the surface of solid materials. Moreover, as optically transparent biomaterials, the content of EpCAM+ EVs could be directly reflected via membrane-based hydrophobic assembly of signaling modules in DFs@EpCAM+ EVs complex, and we found that the amount of EpCAM+ EVs showed greater accuracy in cancer diagnosis than total EVs (88.3 vs 69.7%) and was also higher than the clinically commonly used marker carcinoembryonic antigen (CEA) (88.3 vs 76.7%). In addition, T-EVs could be released by lysis of DFs with the nuclease, gently and easily, keeping high intact and activity of EVs for downstream biological function studies. These results demonstrated that DFs are efficient and nondestructive tools for isolation, detection, and release of T-EVs.

Integrating Reliable Pt-S Bond-Mediated 3D DNA Nanomachine with Magnetic Separation in a Homogeneous Electrochemical Strategy for Exosomal MicroRNA Detection with Low Background and High Sensitivity

Precise and sensitive analysis of exosomal microRNA (miRNA) is of great importance for noninvasive early disease diagnosis, but it remains a great challenge to detect exosomal miRNA in human blood samples because of their small size, high sequence homology, and low abundance. Herein, we integrated reliable Pt-S bond-mediated three-dimensional (3D) DNA nanomachine and magnetic separation in a homogeneous electrochemical strategy for the detection of exosomal miRNA with low background and high sensitivity. The 3D DNA nanomachine was easily prepared via a facile and rapid freezing method, and it was capable of resisting the influence of biothiols, thus endowing it with high stability. Notably, the as-developed magnetic 3D DNA nanomachine not only enabled the detection system to have a low background but also coupled with liposome nanocarriers to synergistically amplify the current signal. Consequently, by ingeniously combining the low background and multiple signal-amplification strategies in homogeneous electrochemical biosensing, highly sensitive detection of exosomal miRNA was successfully achieved. More significantly, with good anti-interference ability, the as-proposed method could effectively discriminate plasma samples from cancer patients and healthy subjects, thus showing a high potential for application in the nondestructive early clinical diagnosis of disease.

Poly-adenine-mediated tetrahedral DNA nanostructure with multiple target-recognition sites for ultrasensitive and rapid electrochemical detection of Aflatoxin B1

Tetrahedral DNA nanostructures (TDNs) are widely used in the development of electrochemical biosensors due to their structural stability, programmability, and strong interfacial orderliness. However, the complex modifications on the electrode and the single vertex target recognition of the TDNs limit their applications in electrochemical biosensing. Herein, we developed a universal detection system based on a novel polyadenine-based tetrahedral DNA nanostructure (ATDN) using Aflatoxin B1 (AFB1) as the model target for analysis. In the absence of target AFB1, the signal probes (SP) modified with ferrocene would be anchored by five aptamers on ATDN. The target capture by aptamers led to a release of SP from the electrode surface, resulting in a significant reduction of the electrochemical signal. This new nanostructure was not only dispensed with multi-step electrode modifications and strong mechanical rigidity but also had five modification sites which enhanced the detection sensitivity for the target. As a result, this biosensor shows good analytical performance in the linear range of 1 fg mL-1 to 1 ng mL-1, exhibiting a low detection limit of 0.33 fg mL-1. Satisfactory accuracy has also been demonstrated through good recoveries (95.2%-98.9%). The proposed new tetrahedral DNA nanostructure can provide a more rapid and sensitive alternative to previous electrochemical sensors based on the conventional TDN. Since DNA sequences can be designed flexibly, the sensing platform in this strategy can be extended to detect various targets in different fields.

A covalent organic framework-derived M1 macrophage mimic nanozyme for precise tumor-targeted imaging and NIR-II photothermal catalytic chemotherapy

Nanoprobes for efficient tumor-targeted imaging and therapy are urgently needed for clinical tumor theranostics. Herein, inspired by the heterogeneity of the tumor microenvironment, we report a covalent organic framework (COF)-derived biomimetic nanozyme for precise tumor-targeted imaging and NIR-II photothermal-catalysis-enhanced chemotherapy (PTCEC). Using a crystalline nanoscale COF as the precursor, a peroxidase-like porous N-doped carbonous nanozyme (PNC) was obtained, which was cloaked with an M1 macrophage cell membrane (M1m) to create a multifunctional biomimetic nanoprobe for tumor-targeted imaging and therapy. The M1m coating enabled the nanoprobe to target cancer cells and tumor tissues for highly efficient tumor imaging and drug delivery. The peroxidase-like activity of the PNC allowed for the conversion of intratumoral H2O2 into toxic ˙OH that synergized with its NIR-II photothermal effect to strengthen the chemotherapy. Therefore, highly efficient tumor-targeted imaging and NIR-II PTCEC were realized with an M1 macrophage mimic nanoprobe. This work provides a feasible tactic for a biomimetic theranostic nanoprobe and will inspire the development of new bioactive nanomaterials for clinical tumor theranostic applications.

Magnetic separation-assisted cluster-amplified versatile fluorescent aptasensors for the sensitive detection of target biomolecules

A sensitive and versatile platform for detecting diverse target biomolecules was developed by combining a magnetic separation module and a fluorescence amplification module in a plug-and-play manner. The magnetic separation module was constructed using magnetic beads (MBs), whose surfaces were modified with aptamer-blocked captor DNAs. The fluorescence amplification module was constructed by loading the fluorescent dye rhodamine 6G (Rh6G) into the pores of mesoporous silica nanoparticles (MSNs). The MSN surfaces were modified with prey DNAs, of which the MSN-near ends hybridized with complementary DNAs (sealing DNAs) to form duplexes to seal the pores, and the free ends were designed to be single-stranded that were complementary to the captor DNAs. Upon binding of targets to their aptamers, the captor DNAs were unblocked and thus were able to hybridize with the prey DNAs, to capture Rh6G-laden MSNs, forming MB-MSN clusters. The clusters were isolated by magnetic separation and heated to dissociate the DNA duplexes, to unseal the MSN pores and release the inner Rh6G; thus a target was converted into a cluster of Rh6G dyes. By simply changing the target aptamers and related DNA connectors, this strategy detected ATP, thrombin, and platelet-derived growth factor BB with detection limits of 2.1 nM, 4.1 pM, and 2.4 pM, respectively. A wide range of targets, high amplification efficiency and universal functional modules endow the aptasensors with good potential as versatile platforms for detecting target molecules in vitro and in medical research.

Exploring the Versatility of Exosomes: A Review on Isolation, Characterization, Detection Methods, and Diverse Applications

Extracellular vesicles (EVs) are crucial mediators of intercellular communication and can be classified based on their physical properties, biomolecular structure, and origin. Among EVs, exosomes have garnered significant attention due to their potential as therapeutic and diagnostic tools. Exosomes are released via fusion of multivesicular bodies on plasma membranes and can be isolated from various biofluids using methods such as differential ultracentrifugation, immune affinity capture, ultrafiltration, and size exclusion chromatography. Herein, an overview of different techniques for exosome characterization and isolation, as well as the diverse applications of exosome detection, including their potential use in drug delivery and disease diagnosis, is provided. Additionally, we discuss the emerging field of exosome detection by sensors, which offers an up-and-coming avenue for point-of-care diagnostic tools development. Overall, this review aims to provide a exhaustive and up-to-date summary of the current state of exosome research.

Employing the Anchor DSPE-PEG as a Redox Probe for Ratiometric Electrochemical Detection of Surface Proteins on Extracellular Vesicles with Aptamers

Quantitative analysis of surface proteins on extracellular vesicles (EVs) has been considered to be a crucial approach for reflecting the status of diseases. Due to the diverse composition of surface proteins on EVs and the interference from nonvesicular proteins, accurately detecting the expression of surface proteins on EVs remains a challenging task. While membrane affinity molecules have been widely employed as EVs capture probes to address this issue, their inherent biochemical properties have not been effectively harnessed. In this paper, we found that the electrochemical redox activity of the DSPE-PEG molecule was diminished upon its insertion into the membrane of EVs. This observation establishes the DSPE-PEG molecule modified on the Au electrode surface as a capture and a redox probe for the electrochemical detection of EVs. By utilizing methylene blue-labeled aptamers, the targeted surface proteins of EVs can be detected by recording the ratio of the oxidation peak current of methylene blue and DSPE-PEG. Without complicated signal amplification, the detection limit for EVs is calculated to be 8.11 × 102 particles/mL. Using this platform, we directly analyzed the expression of CD63 and HER2 proteins on the surface of EVs in human clinical plasma samples, demonstrating its significant potential in distinguishing breast cancer patients from healthy individuals.

A dual-cycle amplification-based electrochemical platform for sensitive detection of tobramycin

BACKGROUND

Tobramycin (TOB), an essential aminoglycoside antibiotic in human life, poses potential threats due to its residues in the environment. The primary concern is the adverse impact of excessive TOB on human kidneys, hearing, and other organs, significantly affecting human health. Constructing a sensitive electrochemical platform for simple and rapid trace detection is crucial. Herein, to enhance the sensitivity of TOB detection in the environment and mitigate the risks associated with residual antibiotics, an ultrasensitive electrochemical aptasensor was developed.

RESULTS

The sensor employs a dual-cycle amplification strategy involving catalytic hairpin assembly (CHA) and exonuclease III (Exo III) for efficient signal amplification. Simultaneously, the electrode performance was optimized by incorporating gold nanowires (AuNWs) onto the surface of reduced graphene oxide (PDA-rGO). Specifically, in the presence of TOB, which binds to the aptamer (Apt), dsDNA dissociates, releasing cDNA to open hairpin 1 (HP1) and initiate the CHA cycle with the participation of hairpin 2 (HP2). Exo III shears HP1 in the HP1/HP2 complex, freeing HP2 to participate in the CHA cycle again. Ultimately, a significant amount of signal label is retained on the electrode by hybridizing with sheared HP1, generating a robust electrical signal.

SIGNIFICANCE

Through the signal amplification strategy, the aptasensor design provides a broad linear range of 0.005-500 nM, with a low detection limit of 0.112 pM for TOB. It is worth mentioning that the aptasensor displayed favorable stability, specificity, and reproducibility, and has been successfully applied to practical samples, demonstrating its utility in practical applications.

Programmable electrochemical biosensing platform based on catalytic hairpin assembly and entropy-driven catalytic cascade amplification circuit

Herein, powerful DNA strand displacement reaction and sensitive electrochemical analysis method were ingeniously integrated to develop a programmable biosensing platform. Using DNA as the detection model, a cascade amplification system based on catalytic hairpin assembly and entropy-driven catalytic was constructed, and the reaction rate and signal amplification effect were significantly improved. The product of the cascade amplification circuit could undergo strand displacement reaction with the signal probe on the electrode surface to obtain sensitive electrochemical signal changes and realize highly sensitive detection of the target. In addition, without redesigning the DNA sequences in the cascade amplification circuit, the by-product strand typically wasted in traditional entropy-driven catalytic reactions can be fully utilized to construct a single-signal output biosensing system and even a dual-signal output ratiometric biosensing platform, improving the detection repeatability and reliability of the system, and expanding the application of DNA strand displacement reaction in electrochemical biosensing. Furthermore, benefiting from the design flexibility of the DNA molecules, the constructed biosensing platform realized the sensitive detection of aptamer substrate (kanamycin as an example) and certain metal ion (mercury as an example) by simply recoding the corresponding recognition sequence, demonstrating the good versatility of the biosensing platform.

Asymmetrically split DNAzyme-based colorimetric and electrochemical dual-modal biosensor for detection of breast cancer exosomal surface proteins

Exosomal surface proteins are potentially useful for breast cancer diagnosis and awareness of risk. However, some detection techniques involving complex operations and expensive instrumentation are limited to advance to clinical applications. To solve this problem, we develop a dual-modal sensor combining naked-eye detection and electrochemical assay of exosomal surface proteins from breast cancer. Most of existing sensors rely on aptamers recognizing exosomes and generating amplified signals at the same time, which require well-designed aptamer probes to avoid difficulties in identifying exosomes. In our work, aptamers not bound by the exosomes can serve as complete templates to induce formation of G quadruplexes. The peroxidase activity of the G-quadruplex/hemin DNAzyme catalyze substrates can generate both color and electrochemical signals. The developed dual-modal sensor offers a remarkable capability to differentiate nonmetastatic, metastatic breast cancer patients, and healthy individuals through the analysis of exosomal surface proteins. The sensor's distinctive features, including its universality, simplicity, and cost-effectiveness, position it as a promising diagnostic tool in breast cancer research and clinical practice.

A dual-model immobilization-free photoelectrochemical/visual colorimetric bioanalysis based on microemulsion self-assemblies mediated multifunctional signal amplification strategy

Herein, a novel silver ion-loaded gold microemulsion assemblies (Au/Ag+ MAs) mediated multifunctional signal amplification strategy was proposed to construct a sensitive immobilization-free photoelectrochemical (PEC)/colorimetric biosensor for carcinoembryonic antigen (CEA) detection. Through the sandwiched reaction among CEA, the CEA aptamer (DNA1) loaded on the Au nanoparticles (NPs) functionalized iron oxide (Fe3O4) nanospheres and another CEA aptamer (DNA2) immobilized on Au/Ag+ MAs, a complex is formed and acquired by magnetic separation. Then, Au/Ag+ MAs of the complex are disassembled into Au NPs and Ag+ ions driven by an acetone response, and the obtained demulsification solution is transferred to the cadmium sulfide/cadmium telluride (CdS/CdTe) photoactive composites modified electrode. Based on the multiple inhibition functions (blocking effect of oleylamine; energy transfer effect of Au NPs; and electron snatching effect of Ag+), the photocurrent of the electrode decreases obviously, resulting in the ultrasensitive detection of CEA (a detection limit of 16 fg mL-1). Interestingly, the ion-exchange reactions between CdS/CdTe composites and Ag+ ions generate silver sulfide/silver telluride (Ag2S/Ag2Te) composites, and a color change of composites can be distinguished directly, leading to a quick visual detection of CEA. Compared with the traditional single-modal assay for CEA, such dual-modal PEC/colorimetric assay is a more accurate and reliable due to different mechanisms and independent signal conversion. This work will offer a new perspective for the applications of various self-assemblies in PEC bioanalysis.

Recent progress in quantitative technologies for the analysis of cancer-related exosome proteins

Exosomes are a kind of extracellular vesicles, which play a significant role in intercellular communication and molecular exchange. Cancer-derived exosomes are potential and ideal biomarkers for the early diagnosis and treatment monitoring of cancers because of their abundant biological information and contribution to the interaction between cancer cells and the tumor microenvironment. However, there are a number of drawbacks, such as low sensitivity and tedious steps, in conventional detection techniques. Furthermore, exosome quantification is not enough to accurately distinguish cancer patients from healthy individuals. Therefore, developing efficient, accurate, and inexpensive exosome surface protein analysis techniques is necessary and critical. In recent years, a considerable number of researchers have presented novel detection strategies in this field. This review summarizes the recent progress in quantitative technologies for the analysis of cancer-related exosome proteins, mainly including the detection methods based on aptamers, nanomaterials, and antibodies, discusses a roadmap for future developments, and aims to offer an innovative perspective of exosome research.

Electrochemical Affinity Biosensors: Pervasive Devices with Exciting Alliances and Horizons Ahead

Electrochemical affinity biosensors are evolving at breakneck speed, strengthening and colonizing more and more niches and drawing unimaginable roadmaps that increasingly make them protagonists of our daily lives. They achieve this by combining their intrinsic attributes with those acquired by leveraging the significant advances that occurred in (nano)materials technology, bio(nano)materials and nature-inspired receptors, gene editing and amplification technologies, and signal detection and processing techniques. The aim of this Perspective is to provide, with the support of recent representative and illustrative literature, an updated and critical view of the repertoire of opportunities, innovations, and applications offered by electrochemical affinity biosensors fueled by the key alliances indicated. In addition, the imminent challenges that these biodevices must face and the new directions in which they are envisioned as key players are discussed.

Enhanced detection of endocrine disrupting chemicals in on-chip microfluidic biosensors using aptamer-mediated bridging flocculation and upconversion luminescence

Exposure to endocrine-disrupting chemicals (EDCs) can lead to detrimental impacts on human health, making their detection a critical issue. A novel approach utilizing on-chip microfluidic biosensors was developed for the simultaneous detection of two EDCs, namely, bisphenol A (BPA) and diethylstilbestrol (DES), based on upconversion nanoparticles doped with thulium (Tm) and erbium (Er), respectively. From the perspective of single nanoparticles, the construction of an active core-inert shell structure enhanced the luminescence of nanoparticles by 2.28-fold (Tm) and 1.72-fold (Er). From the perspective of the nanoparticle population, the study exploited an aptamer-mediated bridging flocculation mechanism and effectively enhanced the upconversion luminescence of biosensors by 8.94-fold (Tm) and 7.10-fold (Er). A chip with 138 tangential semicircles or quarter-circles was designed and simulated to facilitate adequate mixing, reaction, magnetic separation, and detection conditions. The on-chip microfluidic biosensor demonstrated exceptional capabilities for the simultaneous detection of BPA and DES with ultrasensitive detection limits of 0.0076 µg L-1, and 0.0131 µg L-1, respectively. The first reported aptamer-mediated upconversion nanoparticle bridging flocculation provided enhanced luminescence and detection sensitivity for biosensors, as well as offering a new perspective to address the instability of nanobiosensors.

Ratio fluorescence test strip visualized by amino-functionalized metal-organic framework for rapid sensing of glyphosate

As glyphosate is a broad-spectrum herbicide extensively used in agriculture worldwide, rapid glyphosate detection is essential for food safety and human health. Herein, a ratio fluorescence test strip was prepared and coupled with an amino-functionalized bismuth-based metal-organic framework (NH₂-Bi-MOF) that bonded with copper ion for rapid visualization and determination of glyphosate. NH₂-Bi-MOF had excellent fluorescence performance, and the copper ion, a Lewis acid, was selected as the quencher. The strong chelation of glyphosate with copper ion and its quick interaction with NH₂-Bi-MOF would turn on the fluorescence signal, thus enabling the quantitative sensing of glyphosate, with a linear range of 0.10-200 µmol L^-1, and recoveries between 94.8% and 113.5%. The system was then expanded to a ratio fluorescence test strip, in which the fluorescent ring sticker was set as a binding-in self-calibration to reduce errors from the angle and light dependency. The method realized the visual semi-quantitation referring to a standard card, as well as the ratio quantitation using the gray value output with LOD of 0.82 µmol L^-1. And the as-developed test strip was accessible, portable, and reliable, thus offering a platform for the rapid on-site detection of glyphosate and other residual pesticides.

"One suction and one extrusion" mode-based wash-free platform for determination of breast cancer cell-derived exosomes

A simple and wash-free POCT platform based on microcapillary was developed, using breast cancer cell-derived exosomes as a model. This method adopted the "one suction and one extrusion" mode. The hybridized complex of epithelial cell adhesion molecule (EpCAM) aptamer and complementary DNA-horseradish peroxidase conjugate (CDNA-HRP) was pre-modified on the microcapillary's inner surface. "One suction" meant inhaling the sample into the functionalized microcapillary. The exosomes could specifically bind with the EpCAM aptamer on the microcapillary's inner wall, and then the CDNA-HRP complex was released. "One extrusion" referred to squeezing the shedding CDNA-HRP into the 3,3',5,5'-tetramethylbenzidine (TMB)/H₂O₂ solution, and then the enzyme-catalyzed reaction would occur to make the solution yellow using sulfuric acid as the terminator. Therefore, exosome detection could be realized. The limit of detection was 2.69 × 10⁴ particles mL^-1 and the signal value had excellent linearity in the concentration range from 2.75 × 10⁴ to 2.75 × 10⁸ particles⋅mL^-1 exosomes. In addition, the wash-free POCT platform also displayed a favorable reproducibility (RSD = 2.9%) in exosome detection. This method could effectively differentiate breast cancer patients from healthy donors. This work provided an easy-to-operate method for detecting cancer-derived exosomes without complex cleaning steps, which is expected to be applied to breast cancer screening.

Dual-mode colorimetric and homogeneous electrochemical detection of intracellular/extracellular H2O2 based on FeSx/SiO2 nanoparticles with high peroxidase-like activity

Abnormal expression of hydrogen peroxide (H₂O₂) elucidates cell dysfunctions and might induce the occurrence and deterioration of various diseases. However, limited by its ultralow level under pathophysiological conditions, intracellular and extracellular H₂O₂ was difficult to be detected accurately. Herein, a colorimetric and homogeneous electrochemical dual-mode biosensing platform was constructed for intracellular/extracellular H₂O₂ detection based on FeS_x/SiO₂ nanoparticles (FeS_x/SiO₂ NPs) with high peroxidase-like activity. In this design, FeS_x/SiO₂ NPs were synthesized with excellent catalytic activity and stability compared to natural enzymes, which improved the sensitivity and stability of sensing strategy. 3,3',5,5'-Tetramethylbenzidine (TMB), as a multifunctional indicator, was oxidized in the presence of H₂O₂, generated color changes and realized visual analysis. In this process, the characteristic peak current of TMB decreased, which could realize the ultrasensitive detection of H₂O₂ by homogeneous electrochemistry. Accordingly, by integrating visual analysis ability of colorimetry and the high sensitivity of homogeneous electrochemistry, the dual-mode biosensing platform exhibited high accuracy, sensitivity and reliability. The detection limits of H₂O₂ were 0.2 μM (S/N = 3) for the colorimetric method and 2.5 nM (S/N = 3) for the homogeneous electrochemistry assay. Therefore, the dual-mode biosensing platform provided a new opportunity for highly accurate and sensitive detection of intracellular/extracellular H₂O₂.

Streptavidin-Conjugated DNA for the Boronate Affinity-Based Detection of Poly(ADP-Ribose) Polymerase-1 with Improved Sensitivity

This work reports the development of a fluorescence method for the detection of poly(ADP-ribose) polymerase-1 (PARP1), in which a phenylboronic acid-modified fluorescein isothiocyanate dye (FITC-PBA) was used to recognize the formed poly(ADP-ribose) (PAR) polymer. The detection system was designed by conjugating recombinant streptavidin (rSA) with PARP1-specific double-stranded DNA (dsDNA) through streptavidin-biotin interaction. Capture of PARP1 via rSA-biotin-dsDNA allowed for the poly-ADP-ribosylation (PARylation) of both rSA and PARP1 in a homogeneous solution. The resulting rSA-biotin-dsDNA/PAR conjugates were then captured and separated via the commercialized nitrilotriacetic acid-nickel ion-modified magnetic bead (MB-NTA-Ni) through the interaction between NTA-Ni on MB surface and oligohistidine (His₆) tag in rSA. The PAR polymer could capture the dye of FITC-PBA through the borate ester interaction between the boronic acid moiety in PBA and the cis-diol group in ribose, thus causing a decrease in fluorescence signal. The PARylation of streptavidin and the influence of steric hindrance on PARylation efficiency were confirmed using reasonable detection strategies. The method showed a wide linear range (0.01~20 U) and a low detection limit (0.01 U). This work should be valuable for the development of novel biosensors for the detection of poly(ADP-ribose) polymerases and diol-containing species.

Programmable Proteolysis-Activated Transcription for Highly Sensitive Ratiometric Electrochemical Detection of Viral Protease

Viral proteases play a crucial role in viral infection and are regarded as promising targets for antiviral drug development. Consequently, biosensing methods that target viral proteases have contributed to the study of virus-related diseases. This work presents a ratiometric electrochemical sensor that enables highly sensitive detection of viral proteases through the integration of target proteolysis-activated in vitro transcription and the DNA-functionalized electrochemical interface. In particular, each viral protease-mediated proteolysis triggers the transcription of multiple RNA outputs, leading to amplified ratiometric signals on the electrochemical interface. Using the NS3/4A protease of the hepatitis C virus as a model, this method achieves robust and specific NS3/4A protease sensing with sub-femtomolar sensitivity. The feasibility of this sensor was demonstrated by monitoring NS3/4A protease activities in virus-infected cell samples with varying viral loads and post-infection times. This study provides a new approach to analyzing viral proteases and holds the potential for developing direct-acting antivirals and novel therapies for viral infections.

Exogenous interference and autofluorescence-free ratiometric aptasensor for detection of OTA based on dual-colored persistent luminescence nanoparticles

Accurate and sensitive detection of ochratoxin A (OTA) is highly necessary due to its high carcinogenicity, teratogenicity and mutagenicity. Herein, we reported an exogenous interference and autofluorescence-free ratiometric aptasensor based on dual-colored persistent luminescent nanoparticles for precise detection of OTA. Green-emitting ZnGeO:Mn bonded with OTA aptamer and BHQ1-modified complementary base was acted as detection and specific recognition probe (ZGM@BHQ1). Quaternary ammonium modified ZnGaGeO:Cr with red emission was employed as reference probe and further bonded to ZGM@BHQ1 through electrostatic interaction to construct the ratiometric aptasensor. The developed ratiometric aptasensor was free from real-time excitation, external interference and autofluorescence and gave low detection limit of 3.4 pg mL^-1, wide linearity in the range of 0.01-50 ng mL^-1 and high precision of 3.1 % (11 replicate determinations, at 1 ng mL^-1 level). The applicability of the aptasensor was successfully demonstrated by analyzing OTA in in grain samples with recoveries of 97.6 %-105.2 %.

Magnetically Assisted Immobilization-Free Detection of microRNAs Based on the Signal Amplification of Duplex-Specific Nuclease

The double specific nuclease (DSN)-based methods for microRNAs (miRNAs) detection usually require the immobilization of DNA probes on a solid surface. However, such strategies have the drawbacks of low hybridization and cleavage efficiency caused by steric hindrance effect and high salt concentration on the solid surface. Herein, we proposed an immobilization-free method for miRNA detection on the basic of DSN-assisted signal amplification. The biotin- and fluorophore-labeled probes were captured by streptavidin-modified magnetic beads through streptavidin-biotin interactions, thus producing a poor fluorescence signal. Once the DNA probes were hybridized with target miRNA in solution to form DNA-miRNA duplexes, DNA stands in the duplexes would be selectively digested by DSN. The released target miRNA could initiate the next hybridization/cleavage recycling in the homogeneous solution, finally resulting in the release of numerous fluorophore-labeled fragments. The released fluorophores remained in solution and emitted strong fluorescence after treatment by the streptavidin-modified magnetic beads. The immobilization-free method achieved the assays of miRNA-21 with a detection limit down to 0.01 pM. It was employed to evaluate the expression levels of miRNA-21 in different cancer cells with satisfactory results.

Quantification of GPC1(+) Exosomes Based on MALDI-TOF MS In Situ Signal Amplification for Pancreatic Cancer Discrimination and Evaluation

Pancreatic cancer (PC) has a high mortality, with a fairly low five-year survival rate, because of its delayed diagnosis. Recently, liquid biopsy, especially based on exosomes, has attracted vast attention, thanks to its low invasiveness. Herein, we constructed a protocol for pancreatic cancer related Glypican 1 (GPC1) exosome quantification, based on in situ mass spectrometry signal amplification, by utilizing mass tag molecules on gold nanoparticles (AuNPs). Exosomes were extracted and purified by size-exclusion chromatography (SEC), captured by TiO₂ modified magnetic nanoparticles, and then targeted specifically by anti-GPC1 antibody modified on AuNPs. With matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), the signal of PC biomarker, GPC1, was converted to a mass tag signal and amplified. With addition of a certain amount of internal standard molecules modified on AuNPs, the relative intensity ratio of mass tag to internal standard was proportional to the concentration of GPC1(+) exosomes derived from pancreatic cancer cell lines, PANC-1, with good linearity (R² = 0.9945) in a wide dynamic range from 7.1 × 10 to 7.1 × 10⁶ particles/μL. This method was further applied to plasma samples from healthy control (HC) and pancreatic cancer patients with different tumor load, and exhibited a great potential in discriminating diagnosed PC patients from HC, and has the monitoring potential in PC progression.

Label-Free Electrochemical Methods for Disease Detection

Label-free electrochemical biosensing leverages the advantages of label-free techniques, low cost, and fewer user steps, with the sensitivity and portability of electrochemical analysis. In this review, we identify four label-free electrochemical biosensing mechanisms: (a) blocking the electrode surface, (b) allowing greater access to the electrode surface, (c) changing the intercalation or electrostatic affinity of a redox probe to a biorecognition unit, and (d) modulating ion or electron transport properties due to conformational and surface charge changes. Each mechanism is described, recent advancements are summarized, and relative advantages and disadvantages of the techniques are discussed. Furthermore, two avenues for gaining further diagnostic information from label-free electrochemical biosensors, through multiplex analysis and incorporating machine learning, are examined.