A pretreatment-free electrical capacitance biosensor for exosome detection in undiluted serum

Study on Recovery Strategy of Hearing Loss & SGN Regeneration Under Physical Regulation

The World Health Organization (WHO) reports that by 2050, nearly 2.5 billion people are expected to have some degree of hearing loss (HL) and at least 700 million will need hearing rehabilitation. Therefore, there is an urgent need to develop treatment strategies for HL. At present, the main treatment strategies for HL are hearing aids and cochlear implants (CIs), which cannot achieve a radical cure for HL. Relevant studies have shown that the most fundamental treatment strategy for sensorineural hearing loss (SNHL) is to regenerate hair cells and spiral ganglion neurons (SGNs) through stem cells to repair the structure and function of cochlea. In addition, physical stimulation strategies, such as electricity, light, and magnetism have also been used to promote SGN regeneration. This review systematically introduces the classification, principle and latest progress of the existing hearing treatment strategies and summarizes the advantages and disadvantages of each strategy. The research progress of physical regulation mechanism is discussed in detail. Finally, the problems in HL repair strategies are summarized and the future development direction is prospected, which could provide new ideas and technologies for the optimization of hearing treatment strategies and the research of SGN repair and regeneration through physical regulation.

IRTIDP: A simple integrated real-time isolation and detection platform for small extracellular vesicles Glypican-1 in pancreatic cancer patients

Glypican-1 (GPC-1) protein-positive small extracellular vesicles (GPC-1+-sEV) have been proposed as potential biomarkers for early diagnosis of pancreatic cancer. In this study, we present an integrated real-time isolation and detection platform (IRTIDP) to capture and analyze GPC-1+-sEV directly from sera of pancreatic cancer patients. First, CD63 antibody-modified metal-organic framework (MOF) materials were utilized to enrich sEVs with a capture efficiency of 93.93 %. Second, a SERS probe was constructed by Raman reporter 4-MBA and GPC-1 antibody modified SERS active silver nanoparticles (AgNPs), which formed a sandwich complex structure of "MOFs@GPC-1+-sEV@AgNPs-4-MBA" with MOFs-enriched sEVs. The IRTSDP can complete the capture and detection process within 35 min, with a detection limit for 1 GPC-1+-sEV/μL, and linear range between 105∼109 GPC-1+-sEV/mL. Furthermore, this approach has been applied to quantify serum sEV GPC-1 in clinical pancreatic cancer patients. Based on the SERS intensity analysis, pancreatic cancer patients can be distinguished from pancreatic cystadenoma patients and healthy individuals effectively using this innovative platform that provides highly specific and sensitive means for early diagnosis of pancreatic cancer as well as other tumor types.

A rapid field-ready electrical biosensor consisting of bismuthine-derived Au island decorated BiOCl nanosheets for Raphidiopsis raciborskii detection in freshwater

Cyanobacteria play an essential role in nutrient cycling in aquatic ecosystems. However, certain species adversely affect the environment and human health by causing harmful cyanobacterial algal blooms (cyanoHABs) and producing cyanotoxins. To address this issue, continuous cyanoHAB monitoring has been considered; however, a gold standard has not yet been established. In this study, we aimed to develop a dual DNA-targeting capacitive-type biosensor for rapid field-ready monitoring of Raphidiopsis raciborskii, a causative species of cyanoHAB. To enhance the sensing signal, a plate-like Au-BiOCl nanocomposite was synthesized using a spontaneous carbonation process without additional additives. The alternating-current electrothermal flow (ACEF) technique was applied to enable rapid DNA and probe binding within 10 min. The limits of detection (LODs) for R. raciborskii RubisCO large subunit (rbcL) and RNA polymerase beta subunit (rpoB) genes diluted in deionized (DI) water were 4.89 × 10-17 and 3.89 × 10-17 M, respectively. Furthermore, the LODs of R. raciborskii rbcl and rpoB diluted in freshwater containing HAB were 2.55 × 10-16 and 3.84 × 10-16 M, respectively, demonstrating the field-ready applicability of the device. The fabricated cyanobacterial DNA-sensing platform enabled powerful species-specific detection using a small sample volume and low target concentration without a nucleic acid amplification step, dramatically reducing the detection time. This study has considerable implications for detecting HABs, early warning systems, and species-specific environmental monitoring technology.

Miniaturized MXene-based electrochemical biosensors for virus detection

The timely control of infectious diseases can prevent the spread of infections and mitigate the significant socio-economic damage witnessed during recent pandemics. Diagnostic methods play a significant role in detecting highly contagious agents, such as viruses, to prevent further transmission. The emergence of advanced point-of-care techniques offers several advantages over conventional approaches for detecting infectious agents. These techniques are highly sensitive, rapid, can be miniaturized, and are cost-effective. Recently, MXene-based 2D nanocomposites have proven beneficial for fabricating electrochemical biosensors due to their suitable electrical, optical, and mechanical properties. This article covers electrochemical biosensors based on MXene nanocomposite for the detection of viruses, along with the associated challenges and future possibilities. Additionally, we highlight various conventional techniques for the detection of infectious agents, discussing their pros and cons. We delve into the challenges faced during the fabrication of MXene-based biosensors and explore future endeavors. It is anticipated that the information presented in this work will pave the way for the development of Point-of-Care (POC) devices capable of sensitive and selective virus detection, enhancing preparedness for ongoing and future pandemics.

A new label free spiral sensor using impedance spectroscopy to characterize hepatocellular carcinoma in tissue and serum samples

Hepatocellular carcinoma (HCC) stands as the most prevalent form of primary liver cancer, predominantly affecting patients with chronic liver diseases such as hepatitis B or C-induced cirrhosis. Diagnosis typically involves blood tests (assessing liver functions and HCC biomarkers), imaging procedures such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), and liver biopsies requiring the removal of liver tissue for laboratory analysis. However, these diagnostic methods either entail lengthy lab processes, require expensive imaging equipment, or involve invasive techniques like liver biopsies. Hence, there exists a crucial need for rapid, cost-effective, and noninvasive techniques to characterize HCC, whether in serum or tissue samples. In this study, we developed a spiral sensor implemented on a printed circuit board (PCB) technology that utilizes impedance spectroscopy and applied it to 24 tissues and sera samples as proof of concept. This newly devised circuit has successfully characterized HCC and normal tissue and serum samples. Utilizing the distinct dielectric properties between HCC cells and serum samples versus the normal samples across a specific frequency range, the differentiation between normal and HCC samples is achieved. Moreover, the sensor effectively characterizes two HCC grades and distinguishes cirrhotic/non-cirrhotic samples from tissue specimens. In addition, the sensor distinguishes cirrhotic/non-cirrhotic samples from serum specimens. This pioneering study introduces Electrical Impedance Spectroscopy (EIS) spiral sensor for diagnosing HCC and liver cirrhosis in clinical serum-an innovative, low-cost, rapid (< 2 min), and precise PCB-based technology without elaborate sample preparation, offering a novel non-labeled screening approach for disease staging and liver conditions.

Printed circuit boards: system automation and alternative matrix for biosensing

Circuit integration has revolutionized the diagnostic sector by improving the sensing ability and rapidity of biosensors. Bioelectronics has led to the development of point-of-care (PoC) devices, offering superior performance compared with conventional biosensing systems. These devices have lower production costs, are smaller, and have greater reproducibility, enabling the construction of compact sensing modules. Flexible upgrades to the fabrication pattern of the printed circuit board (PCB) remains the most reliable and consistent means so far, offering portability, wearability, a lower detection limit, and smart output integration to these devices. This review summarizes the advances in PCB technology for biosensing devices for introducing automation and their emerging application as an alternative matrix material for detecting various analytes.

Magnetically Controlled Photothermal, Colorimetric, and Fluorescence Trimode Assay for Gastric Cancer Exosomes Based on Acid-Induced Decomposition of CP/Mn-PBA DSNBs

The accurate quantification of cancer-derived exosomes, which are emerging as promising noninvasive biomarkers for liquid biopsies in the early diagnosis of cancer, is becoming increasingly imperative. In our work, we developed a magnetically controlled photothermal, colorimetric, and fluorescence trimode aptasensor for human gastric cancer cell (SGC-7901)-derived exosomes. This sensor relied on CP/Mn-PBA DSNBs nanocomposites, created by decorating copper peroxide (CP) nanodots on polyethyleneimine-modified manganese-containing Prussian blue analogues double-shelled nanoboxes (PEI-Mn-PBA DSNBs). Through self-assembly, we attached CD63 aptamer-labeled CP/Mn-PBA DSNBs (Apt-CP/Mn-PBA DSNBs) to complementary DNA-labeled magnetic beads (cDNA-MB). During exosome incubation, these aptamers preferentially formed complexes with exosomes, and we efficiently removed the released CP/Mn-PBA DSNBs by using magnetic separation. The CP/Mn-PBA DSNBs exhibited high photoreactivity and photothermal conversion efficiency under near-infrared (NIR) light, leading to temperature variations under 808 nm irradiation, correlating with different exosome concentrations. Additionally, colorimetric detection was achieved by monitoring the color change in a 3,3',5,5'-tetramethylbenzidine (TMB) system, facilitated by PEI modification, NIR-enhanced peroxidase-like activity of CP/Mn-PBA DSNBs and their capacity to generate Cu2+ and H2O2 under acidic conditions. Moreover, in the presence of Cu2+ and ascorbic acid (AA), DNA sequences could form dsDNA-templated copper nanoparticles (CuNPs), which emitted strong fluorescence at around 575 nm. Increasing exosome concentrations correlated with decreases in temperature, absorbance, and fluorescence intensity. This trimode biosensor demonstrated satisfactory ability in differentiating gastric cancer patients from healthy individuals using human serum samples.

Capacitive biosensors for label-free and ultrasensitive detection of biomarkers

Capacitive biosensors are label-free capacitors that can detect biomarkers with the outstanding advantages of simplicity, low cost, and ultrahigh sensitivity. A typical capacitive biosensor consists of a bioreceptor and a transducer, where the bioreceptor captures the biomarker to form a bioreceptor/biomarker conjugate and the transducer generates a detectable signal. In general, antibodies, aptamers, or proteins are exploited as the bioreceptor, while various electrodes including carbon electrodes (CEs), gold electrodes (AuEs), or interdigitated electrodes (IDEs) may serve as the transducer. Because the formation of bioreceptor/biomarker conjugates often leads to a change in capacitance, the capacitive signal is then employed for biomarker detection. This review summarizes recent advances in capacitive biosensors for the detection of biomarkers over the last five years. With a focus on the three common types of bioreceptors, i.e., antibodies, aptamers, and proteins, capacitive biosensors using CEs, AuEs, and IDEs as the transducers are discussed in detail. The immobilization of bioreceptors and signal amplification strategies are described to provide a robust overview of capacitive biosensors for biomarker detection. In addition, analytical methods and future prospects are given to support the application of capacitive biosensors.

Application of 3D printing technology in tumor diagnosis and treatment

3D printing technology is an increasing approach consisting of material manufacturing through the selective incremental delamination of materials to form a 3D structure to produce products. This technology has different advantages, including low cost, short time, diversification, and high precision. Widely adopted additive manufacturing technologies enable the creation of diagnostic tools and expand treatment options. Coupled with its rapid deployment, 3D printing is endowed with high customizability that enables users to build prototypes in shorts amounts of time which translates into faster adoption in the medical field. This review mainly summarizes the application of 3D printing technology in the diagnosis and treatment of cancer, including the challenges and the prospects combined with other technologies applied to the medical field.

Localized Imaging of Programmed Death-Ligand 1 on Individual Tumor-Derived Extracellular Vesicles for Prediction of Immunotherapy Response

Programmed death-ligand 1 (PD-L1) on tumor-derived small extracellular vesicles (EVs) is a biomarker for prediction of the immunotherapy response. However, conventional bulk measurement can hardly analyze the expression of PD-L1 on individual tumor-derived EVs. Herein, a method for localized imaging of tumor-derived individual EVs PD-L1 (LITIE) is developed. In this assay, EVs in plasma were directly captured on a biochip. Then the liposome-mediated membrane fusion strategy was used to image miR-21 in EVs to discriminate miR-21-positive EVs from the whole EVs populations. Subsequently, the primer exchange reaction (PER) is applied to generate localized and amplified fluorescent signals for imaging PD-L1 on identified tumor-derived EVs. When applied in clinical sample tests, the LITIE assay could effectively distinguish breast cancer patients from healthy donors or patients with benign tumors. Interestingly, in a mice melanoma model, the LITIE assay showed the ability to predict immunotherapy response even before drug treatment. Thus, we think the strategy of measuring individual tumor-derived EVs PD-L1 could serve as an alternative way for screening clinical responders suitable for immunotherapy.

Current research status of tumor cell biomarker detection

With the annual increases in the morbidity and mortality rates of tumors, the use of biomarkers for early diagnosis and real-time monitoring of tumor cells is of great importance. Biomarkers used for tumor cell detection in body fluids include circulating tumor cells, nucleic acids, protein markers, and extracellular vesicles. Among them, circulating tumor cells, circulating tumor DNA, and exosomes have high potential for the prediction, diagnosis, and prognosis of tumor diseases due to the large amount of valuable information on tumor characteristics and evolution; in addition, in situ monitoring of telomerase and miRNA in living cells has been the topic of extensive research to understand tumor development in real time. Various techniques, such as enzyme-linked immunosorbent assays, immunoblotting, and mass spectrometry, have been widely used for the detection of these markers. Among them, the detection of tumor cell markers in body fluids based on electrochemical biosensors and fluorescence signal analysis is highly preferred because of its high sensitivity, rapid detection and portable operation. Herein, we summarize recent research progress in the detection of tumor cell biomarkers in body fluids using electrochemical and fluorescence biosensors, outline the current research status of in situ fluorescence monitoring and the analysis of tumor markers in living cells, and discuss the technical challenges for their practical clinical application to provide a reference for the development of new tumor marker detection methods.

Fabrication of graphene oxide-based pretreatment filter and Electrochemical-CRISPR biosensor for the field-ready cyanobacteria monitoring system

Microcystis aeruginosa (M. aeruginosa) cause the eutrophication of lakes and rivers. To effectively control the overgrowth of M. aeruginosa, a suitable measurement method should be required in the aquatic fields. To address this, we developed a field-ready cyanobacterial pretreatment device and an electrochemical clustered regularly interspaced short palindromic repeats (EC-CRISPR) biosensor. The cyanobacterial pretreatment device consists of a syringe, glass bead, and graphene oxide (GO) bead. Then, the M. aeruginosa dissolved in the freshwater sample was added to fabricated filter. After filtration, the purified gene was loaded onto a CRISPR-based electrochemical biosensor chip to detect M. aeruginosa gene fragments. The biosensor was composed of CRISPR/Cpf1 protein conjugated with MXene on an Au microgap electrode (AuMGE) integrated into a printed circuit board (PCB). This AuMGE/PCB system maximizes the signal-to-noise ratio, which controls the working and counter electrode areas requiring only 3 μL samples to obtain high reliability. Using the extracted M. aeruginosa gene with a pre-treatment filter, the CRISPR biosensor showed a limit of detection of 0.089 pg/μl in fresh water. Moreover, selectivity test and matrix condition test carried out using the EC-CRISPR biosensor. These handheld pre-treatment kit and biosensors can enable field-ready detection of CyanoHABs.

Molybdenum Disulfide as Tunable Electrochemical and Optical Biosensing Platforms for Cancer Biomarker Detection: A Review

Cancer is a common illness with a high mortality. Compared with traditional technologies, biomarker detection, with its low cost and simple operation, has a higher sensitivity and faster speed in the early screening and prognosis of cancer. Therefore, extensive research has focused on the development of biosensors and the construction of sensing interfaces. Molybdenum disulfide (MoS2) is a promising two-dimensional (2D) nanomaterial, whose unique adjustable bandgap shows excellent electronic and optical properties in the construction of biosensor interfaces. It not only has the advantages of a high catalytic activity and low manufacturing costs, but it can also further expand the application of hybrid structures through different functionalization, and it is widely used in various biosensors fields. Herein, we provide a detailed introduction to the structure and synthesis methods of MoS2, and explore the unique properties and advantages/disadvantages exhibited by different structures. Specifically, we focus on the excellent properties and application performance of MoS2 and its composite structures, and discuss the widespread application of MoS2 in cancer biomarkers detection from both electrochemical and optical dimensions. Additionally, with the cross development of emerging technologies, we have also expanded the application of other emerging sensors based on MoS2 for early cancer diagnosis. Finally, we summarized the challenges and prospects of MoS2 in the synthesis, functionalization of composite groups, and applications, and provided some insights into the potential applications of these emerging nanomaterials in a wider range of fields.

Extended-Gate Field-Effect Transistor Consisted of a CD9 Aptamer and MXene for Exosome Detection in Human Serum

Cancer progresses silently to the terminal stage of the impossible operable condition. There are many limitations in the treatment options of cancer, but diagnosis in an early stage can improve survival rates and low recurrence. Exosomes are the biomolecules released from cancer cells and are promising candidates for clinical diagnosis. Among them, the cluster of differentiation 9 (CD9) protein is an important exosomal biomarker that can be used for exosome determination. Therefore, here, a CD9 aptamer was first synthesized and applied to an extended-gate field-effect transistor (EGFET)-type biosensor containing a disposable sensing membrane to suggest the possibility of detecting exosomes in a clinical environment. Systematically evaluating ligands using the exponential enrichment (SELEX) technique was performed to select nucleic acid sequences that can specifically target the CD9 protein. Exosomes were detected according to the electrical signal changes on a membrane, which is an extended gate using an Au microelectrode. The fabricated biosensor showed a limit of detection (LOD) of 10.64 pM for CD9 proteins, and the detection range was determined from 10 pM to 1 μM in the buffer. In the case of the clinical test, the LOD and detection ranges of exosomes in human serum samples were 6.41 × 102 exosomes/mL and 1 × 103 to 1 × 107 exosomes/mL, respectively, showing highly reliable results with low error rates. These findings suggest that the proposed aptasensor can be a powerful tool for a simple and early diagnosis of exosomes.

Synthesis of Isolated DNA Aptamer and Its Application of AC-Electrothermal Flow-Based Rapid Biosensor for the Detection of Dengue Virus in a Spiked Sample

Dengue fever is an infectious disease caused by the dengue virus (DENV) and is transmitted by mosquitoes in tropical and subtropical regions. The early detection method at a low cost is essential. To address this, we synthesized the isolated DENV aptamer for fabricating a rapid electrochemical biosensor on a Au interdigitated microgap electrode (AuIMGE). The DENV aptamers were generated using the SELEX (systemic evolution of ligands by exponential enrichment) method for binding to DENV surface envelope proteins. To reduce the manufacturing cost, unnecessary nucleotide sequences were excluded from the isolation process of the DENV aptamer. To reduce the detection time, the alternating current electrothermal flow (ACEF) technique was applied to the fabricated biosensor, which can shorten the detection time to 10 min. The performance of the biosensor was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In the diluted DENV protein solution, the linear range of the concentrations was from 1 pM to 1 μM and the LOD was 76.7 fM. Moreover, the proposed biosensor detected DENV in a diluted spiked sample at a linear range of 10-6 to 106 TCID50/mL, while the detection performance was proven with an LOD of 1.74 × 10-7 TCID50/mL along with high selectivity.

Graphene Sensor Arrays for Rapid and Accurate Detection of Pancreatic Cancer Exosomes in Patients' Blood Plasma Samples

Biosensors based on graphene field effect transistors (GFETs) have the potential to enable the development of point-of-care diagnostic tools for early stage disease detection. However, issues with reproducibility and manufacturing yields of graphene sensors, but also with Debye screening and unwanted detection of nonspecific species, have prevented the wider clinical use of graphene technology. Here, we demonstrate that our wafer-scalable GFETs array platform enables meaningful clinical results. As a case study of high clinical relevance, we demonstrate an accurate and robust portable GFET array biosensor platform for the detection of pancreatic ductal adenocarcinoma (PDAC) in patients' plasma through specific exosomes (GPC-1 expression) within 45 min. In order to facilitate reproducible detection in blood plasma, we optimized the analytical performance of GFET biosensors via the application of an internal control channel and the development of an optimized test protocol. Based on samples from 18 PDAC patients and 8 healthy controls, the GFET biosensor arrays could accurately discriminate between the two groups while being able to detect early cancer stages including stages 1 and 2. Furthermore, we confirmed the higher expression of GPC-1 and found that the concentration in PDAC plasma was on average more than 1 order of magnitude higher than in healthy samples. We found that these characteristics of GPC-1 cancerous exosomes are responsible for an increase in the number of target exosomes on the surface of graphene, leading to an improved signal response of the GFET biosensors. This GFET biosensor platform holds great promise for the development of an accurate tool for the rapid diagnosis of pancreatic cancer.

Fabrication of Rapid Electrical Pulse-Based Biosensor Consisting of Truncated DNA Aptamer for Zika Virus Envelope Protein Detection in Clinical Samples

Zika virus (ZV) infection causes fatal hemorrhagic fever. Most patients are unaware of their symptoms; therefore, a rapid diagnostic tool is required to detect ZV infection. To solve this problem, we developed a rapid electrical biosensor composed of a truncated DNA aptamer immobilized on an interdigitated gold micro-gap electrode and alternating current electrothermal flow (ACEF) technique. The truncated ZV aptamer (T-ZV apt) was prepared to reduce the manufacturing cost for biosensor fabrication, and it showed binding affinity similar to that of the original ZV aptamer. This pulse-voltammetry-based biosensor was composed of a T-ZV apt immobilized on an interdigitated micro-gap electrode. Atomic force microscopy was used to confirm the biosensor fabrication. In addition, the optimal biosensor performance conditions were investigated using pulse voltammetry. ACEF promoted aptamer-target binding, and the target virus envelope protein was detected in the diluted serum within 10 min. The biosensor waveform increased linearly as the concentration of the Zika envelope in the serum increased, and the detection limit was 90.1 pM. Our results suggest that the fabricated biosensor is a significant milestone for rapid virus detection.

Aptamer-functionalized capacitive biosensors

The growing use of aptamers as target recognition elements in label-free biosensing necessitates corresponding transducers that can be used in relevant environments. While popular in many fields, capacitive sensors have seen relatively little, but growing use in conjunction with aptamers for sensing diverse targets. Few reports have shown physiologically relevant sensitivity in laboratory conditions and a cohesive picture on how target capture modifies the measured capacitance has been lacking. In this review, we assess the current state of the field in three areas: small molecule, protein, and cell sensing. We critically analyze the proposed hypotheses on how aptamer-target capture modifies the capacitance, as many mechanistic postulations appear to conflict between published works. As the field matures, we encourage future works to investigate individual aptamer-target interactions and to interrogate the physical mechanisms leading to measured changes in capacitance. To this point, we provide recommendations on best practices for developing aptasensors with a particular focus on considerations for biosensing in clinical settings.

Peptide-anchored biomimetic interface for electrochemical detection of cardiomyocyte-derived extracellular vesicles

Cardiomyocyte-derived extracellular vesicles (EVs) are a promising class of biomarkers that can advance the diagnosis of many kinds of cardiovascular diseases. Herein, we develop a new electrochemical method for the feasible detection of cardiomyocyte-derived EVs in biological fluids. The core design of the method is the fabrication of a peptide-anchored biomimetic interface consisting of a lipid bilayer and peptide probes. On the one hand, the lipid bilayer provides excellent antifouling ability to the electrode interface and facilitates the anchoring of peptide probes. On the other hand, the peptide probes equip the electrode interface with excellent binding capability and affinity to CD172a, a specific marker of cardiomyocyte-derived EVs, thus enabling the efficient and selective detection of target EVs. Taking EVs derived from the heart myoblast cells H9C2 as the model target, the method displays a wide linear detection range from 1 × 10³ to 1 × 10⁸ particles/mL with a desirable detection limit of 132 particles/mL. Furthermore, the method shows good performance in biological fluids such as serum, and thus may have great potential for practical use in the diagnosis of cardiovascular diseases.

Rapid electrochemical biosensor composed of DNA probe/iridium nanoparticle bilayer for Aphanizomenon flos-aquae detection in fresh water

Toxic cyanobacteria pose a serious threat to aquatic ecosystems and require adequate detection and control systems. Aphanizomenon flos-aquae is a harmful cyanobacterium that produces the toxicant saxitoxin. Therefore, it is necessary to detect the presence of A. flos-aquae in lakes and rivers. We proposed a rapid electrochemical biosensor composed of DNA primer/iridium nanoparticles (IrNP) bilyer for the detection of A. flos-aquae in freshwater. The extracted A. flos-aquae gene (rbcL-rbcX) is used as a target, and it was fixed to the electrode using a 5'-thiolated DNA primer (capture probe). Then, Avidin@IrNPs complex for amplification of electrical signals was bound to the target through a 3'-biotinylated DNA primer (detection probe). To rapidly detect the target, an alternating current electrothermal flow technique was introduced in the detection step, which could reduce the detection time to within 20 min. To confirm the biosensor fabrication, atomic force microscopy was used to investigate the surface morphology. To evaluate the biosensor performance, cyclic voltammetry and electrochemical impedance spectroscopy were used. The target gene was detected at a concentration of 9.99 pg/mL in tap water, and the detection range was 0.1 ng/mL to 10³ ng/mL with high selectivity. Based on the combined system, we employed A. flos-aquae in tap water. This rapid cyanobacteria detection system is a powerful tool for CyanoHABs in the field.

Assembling Vertical Nanogap Arrays with Nanoentities for Highly Sensitive Electrical Biosensing

Nanogap biosensors have emerged as promising platforms for detecting and measuring biochemical substances at low concentrations. Although the nanogap biosensors provide high sensitivity, low limit of detection (LOD), and enhanced signal strength, it requires arduous fabrication processes and costly equipment to obtain micro/nanoelectrodes with extremely narrow gaps in a controlled manner. In this work, we report the novel design and fabrication processes of vertical nanogap structures that can electrically detect and quantify low-concentration biochemical substances. Approximately 40 nm gaps are facilely created by magnetically assembling antibody-coated nanowires onto a nanodisk patterned between a pair of microelectrodes. Analyte molecules tagged with conductive nanoparticles are captured and bound to nanowires and bridge over the nanogaps, which consequently causes an abrupt change in the electrical conductivity between the microelectrodes. Using biotin and streptavidin as model antibodies and analytes, we demonstrated that our nanogap biosensors can effectively measure the protein analytes with the LOD of ∼18 pM. The outcome of this research could inspire the design and fabrication of nanogap devices and nanobiosensors, and it would have a broad impact on the development of microfluidics, biochips, and lab-on-a-chip architectures.

Recent Developments in DNA-Nanotechnology-Powered Biosensors for Zika/Dengue Virus Molecular Diagnostics

Zika virus (ZIKV) and dengue virus (DENV) are highly contagious and lethal mosquito-borne viruses. Global warming is steadily increasing the probability of ZIKV and DENV infection, and accurate diagnosis is required to control viral infections worldwide. Recently, research on biosensors for the accurate diagnosis of ZIKV and DENV has been actively conducted. Moreover, biosensor research using DNA nanotechnology is also increasing, and has many advantages compared to the existing diagnostic methods, such as polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). As a bioreceptor, DNA can easily introduce a functional group at the 5' or 3' end, and can also be used as a folded structure, such as a DNA aptamer and DNAzyme. Instead of using ZIKV and DENV antibodies, a bioreceptor that specifically binds to viral proteins or nucleic acids has been fabricated and introduced using DNA nanotechnology. Technologies for detecting ZIKV and DENV can be broadly divided into electrochemical, electrical, and optical. In this review, advances in DNA-nanotechnology-based ZIKV and DENV detection biosensors are discussed.

Selection of DNA aptamer and its application as an electrical biosensor for Zika virus detection in human serum

Zika virus is a highly infectious virus that is part of the flavivirus group. Precise diagnosis of the Zika virus is significant issue for controlling a global pandemic after the COVID-19 era. For the first time, we describe a zika virus aptamer-based electrical biosensor for detecting Zika virus in human serum. The electrical biosensor composed of a Zika virus aptamer/MXene nanoparticle heterolayer on Au micro-gap electrode (AuMGE)/print circuit board (PCB) system. The Zika virus aptamer was designed to bind the envelope protein of the Zika virus by systematic evolution of ligands by exponential enrichment (SELEX) technique. The binding affinity of the aptamer was determined by fluorescence. For improving the sensor signal sensitivity, Ti₃C₂T_x MXene was introduced to surface of Au micro-gap electrode (AuMGE). The immobilization process was confirmed by atomic force microscopy (AFM). The prepared aptamer/MXene immobilized on AuMGE can detect the Zika virus through capacitance change according to the target concentration. The capacitance signal from the biosensor increased linearly according to increment of envelope proteins in the human serum. The limit of detection was determined to 38.14 pM, and target proteins could be detected from 100 pM to 10 μM. Thus, the developed electrical aptabiosensor can be a useful tool for Zika virus detection.

Introduction of Nanomaterials to Biosensors for Exosome Detection: Case Study for Cancer Analysis

Exosomes have been gaining attention for early cancer diagnosis owing to their biological functions in cells. Several studies have reported the relevance of exosomes in various diseases, including pancreatic cancer, retroperitoneal fibrosis, obesity, neurodegenerative diseases, and atherosclerosis. Particularly, exosomes are regarded as biomarkers for cancer diagnosis and can be detected in biofluids, such as saliva, urine, peritoneal fluid, and blood. Thus, exosomes are advantageous for cancer liquid biopsies as they overcome the current limitations of cancer tissue biopsies. Several studies have reported methods for exosome isolation, and analysis for cancer diagnosis. However, further clinical trials are still required to determine accurate exosome concentration quantification methods. Recently, various biosensors have been developed to detect exosomal biomarkers, including tumor-derived exosomes, nucleic acids, and proteins. Among these, the exact quantification of tumor-derived exosomes is a serious obstacle to the clinical use of liquid biopsies. Precise detection of exosome concentration is difficult because it requires clinical sample pretreatment. To solve this problem, the use of the nanobiohybrid material-based biosensor provides improved sensitivity and selectivity. The present review will discuss recent progress in exosome biosensors consisting of nanomaterials and biomaterial hybrids for electrochemical, electrical, and optical-based biosensors.

Sensing gastric cancer exosomes with MoS2-based SERS aptasensor

Exosomes have been widely used in early cancer diagnosis as promising cancer biomarkers due to their abundant tumor-specific molecular information. In this study, we developed a sensitive and straightforward surface-enhanced Raman scattering (SERS) aptasensor to detect exosomes based on gold nanostars-decorated molybdenum disulfide (MoS₂) nanocomposites (MoS₂-AuNSs). ROX-labeled aptamers (ROX-Apt) were assembled on MoS₂-AuNSs surface as recognition probes that specifically bind with transmembrane protein CD63 (a representative surface marker on exosomes). Thus obvious ROX Raman signals were obtained through the synergistic Raman enhancement effect of AuNSs and MoS₂ nanosheet. In presence of exosomes, ROX-Apt is preferentially tethered onto exosomes and released from the surface of nanocomposites, resulting in a decrease of the SERS signal. Expectedly, the as-fabricated SERS aptasensor was capable of detecting exosomes in a wide range from 55 to 5.5 × 10⁵ particles μL^-1 with a detection limit of 17 particles μL^-1. Moreover, the aptasensor exhibited accepted stability and potential clinical applicability.

Recent Advances in DNA Nanotechnology for Plasmonic Biosensor Construction

Since 2010, DNA nanotechnology has advanced rapidly, helping overcome limitations in the use of DNA solely as genetic material. DNA nanotechnology has thus helped develop a new method for the construction of biosensors. Among bioprobe materials for biosensors, nucleic acids have shown several advantages. First, it has a complementary sequence for hybridizing the target gene. Second, DNA has various functionalities, such as DNAzymes, DNA junctions or aptamers, because of its unique folded structures with specific sequences. Third, functional groups, such as thiols, amines, or other fluorophores, can easily be introduced into DNA at the 5′ or 3′ end. Finally, DNA can easily be tailored by making junctions or origami structures; these unique structures extend the DNA arm and create a multi-functional bioprobe. Meanwhile, nanomaterials have also been used to advance plasmonic biosensor technologies. Nanomaterials provide various biosensing platforms with high sensitivity and selectivity. Several plasmonic biosensor types have been fabricated, such as surface plasmons, and Raman-based or metal-enhanced biosensors. Introducing DNA nanotechnology to plasmonic biosensors has brought in sight new horizons in the fields of biosensors and nanobiotechnology. This review discusses the recent progress of DNA nanotechnology-based plasmonic biosensors.

Programmable DNA-Fueled Electrochemical Analysis of Lung Cancer Exosomes

Molecular diagnostics devoted to discover and monitor new biomarkers is gaining increasing attention in clinical diagnosis. In this work, a programmable DNA-fueled electrochemical analysis strategy is designed for the determination of an emerging biomarker in lung cancer, PD-L1-expressing exosomes. Specifically, PD-L1-expressing exosomes are first enriched onto magnetic beads functionalized with PD-L1 antibody and are able to interact with cholesterol-modified hairpin templates. Then, programmable DNA synthesis starts from the hairpin template-triggered primer exchange reaction and generates a large number of extension products to activate the trans-cleavage activity of CRISPR-Cas12a. After that, CRISPR-Cas12a-catalyzed random cleavage boosts the degradation of methylene blue-labeled signaling strands, so electro-active methylene blue molecules can be enriched onto a cucurbit[7]uril-modified electrode for quantitative determination. Our method demonstrates high sensitivity and specificity toward electrochemical analysis of PD-L1-expressing exosomes in the range from 10³ to 10⁹ particles mL^-1 with a low detection limit of 708 particles mL^-1. When applied to clinical samples, our method reveals an elevated level of circulating PD-L1-expressing exosomes in lung cancer patients, especially for those at the advanced stages. Therefore, our method may provide new insight into liquid biopsy for better implementation of immunotherapy in lung cancer in the future.

Exosome-based drug delivery systems and their therapeutic applications

In the past few decades, scientists have actively worked on developing effective drug delivery systems (DDSs) as means to control life-threatening diseases and challenging illnesses.