Near-Infrared-to-Ultraviolet Light-Mediated Photoelectrochemical Aptasensing Platform for Cancer Biomarker Based on Core-Shell NaYF4:Yb,Tm@TiO2 Upconversion Microrods

Directly profiling intact Staphylococcus aureus in water and foods via enzymatic cleavage aptasensor

Staphylococcus aureus (S. aureus) causes serious food-borne diseases, and tools able to directly profile intact S. aureus would greatly facilitate food safety and public health. Herein, we proposed a biosensing platform for culture-independent and separation-free profiling S. aureus, thus allow us to directly detect intact S. aureus in complex samples. The binding protection effect of aptamer-cell complex was introduced to construct the aptasensor, and it allowed to eliminate the optimization of aptamer probe sequences. The proposed aptasensor, terms enzymatic cleavage aptasensor could achieve a sensitive (a detection limit of 64 CFU/mL) and broad-concentration quantification (dynamic range 10²-10⁷ CFU/mL) of S. aureus. Furthermore, it could specifically identify intact S. aureus in complex samples, and the quantifying of S. aureus was achieved in tap water, milk and porker with high precision. Therefore, enzymatic cleavage aptasensor could be a good candidate for on-site biosensing platform of S. aureus, as well as other pathogens by replacing the aptamer sequences.

One-Step Synthesis of Methylene Blue-Encapsulated Zeolitic Imidazolate Framework for Dual-Signal Fluorescent and Homogeneous Electrochemical Biosensing

In vitro diagnosis requires target biomarkers to be reliably detected at an ultralow level. A dual-signal strategy permits self-calibration to overcome the interferences of experimental and environmental factors, and thus is regarded as a promising approach. However, currently reported works mainly concentrated on the same forms of energy of output signals. Herein, we propose a one-step strategy for synthesis of methylene blue-encapsulated zeolitic imidazolate framework-90 (MB@ZIF-90) with high loading, unique dual-signal property, exceptional recognition capability, and good stability, and we further pioneer MB@ZIF-90 as a dual-signal biosensor for label-free, enzyme-free, and ultrasensitive detection of adenosine triphosphate (ATP) by integration of fluorescence and homogeneous electrochemical techniques. The recognition of MB@ZIF-90 by target ATP spurs the decomposition of ZIF-90, subsequently permitting MB to be released into a supernatant. As compared to the case where ATP does not exist, obviously increased intensities in fluorescence and differential pulse voltammetry current are observed and both signals are directly proportional to ATP concentrations. Thus, the MB@ZIF-90-based biosensor achieved dual-signal detection of ATP in an ultrasensitive manner and displayed a more reliable diagnosis result than previously reported ATP biosensors. This dual-signal strategy provides a new opportunity to develop high-performance biosensors for in vitro diagnosis and demonstrates great potential for future applications in bioinformatics and clinical medicine.

A novel photoelectrochemical sensor based on tailoring printable mesoscopic chip for fast and real-time phospholipids oxidation detection

The detection of phospholipids oxidation is important for meat control and disease prevention. In this paper, a photoelectrochemical sensor based on printable mesoscopic chip (PMC) for fast and real-time monitoring phospholipids oxidation was designed and fabricated. TiO2, ZrO2 and carbon films of PMC were screen-printed onto the FTO glass layer by layer. The PMC and the feasibility for determination of phospholipids oxidation were investigated by scanning electron microscope (SEM), UV-vis spectroscopy, cyclic voltammograms (CVs) and electrochemical impedance spectroscopy (EIS), etc. The short circuit current (Jsc) was used as a signal current, which would decrease if phospholipids in PMC were undergoing oxidation for the change of electrical properties. Compared with other methods, phospholipids in PMC did not require pretreatment, and the process was nondestructive and real-time. Meanwhile, this method showed high sensitivity and good selectivity. The fabricating process of PMC is simple, and the costs are low, relatively.

Superparamagnetic Nanostructures for Split-Type and Competitive-Mode Photoelectrochemical Aptasensing

Photoelectrochemical sensing has developed rapidly in the past decade because of its inherent advantages of economic devices and low background noise. However, traditional assembly of photoelectric beacons, probes, and targets on the ITO electrode solid-liquid interface inevitably leads to time-consuming, limited selectivity, poor stability, and nonreproducibility. To overcome these drawbacks, in this work, a unique split-type PEC aptasensor for carcinoembryonic antigen (CEA) was developed in virtue of the sandwich-like structure comprised of magnetic-optical Fe₃O₄@SiO₂@CdS-DNA₁, CEA aptamer, and signal element SiO₂-Au-DNA₂. The sandwich-like structure is easily formed in the liquid phase and can be triggered by competition from low-abundance CEA, resulting in dissociation. By further photocurrent measurement in pure phosphate buffer saline (PBS), coexisting species can be effectively removed from the modified electrode, improving selectivity, stability, and repeatability. These advantages benefit from the preparation of uniform and monodispersed Fe₃O₄@SiO₂@CdS and SiO₂-Au particles, DNAs assembly, and an elegant design. Additionally, the as-designed signal-on PEC aptasensor is highly sensitive, short time-consuming, and economical, enabling the detection of CEA in serum specimens. It not only provides an alternative to CEA immunosensors, but also paves the way for high-performance PEC aptasensors.

A novel bioassay for the monitoring of carcinoembryonic antigen in human biofluid using polymeric interface and immunosensing method

Carcinoembryonic antigen (CEA) is a member of a family of cell surface glycoproteins. Recognition of CEA is needed to monitor the physiological status of the patient for treatment and also it is important to assess the severity of the disease. In this work, we reported a novel sandwich-type electrochemical immunosensor based on gold nanoparticles functionalized cysteamine-glutaraldehyde (AuNPs-CysA-GA) and it successfully designed to detection of the CEA biomarker in a human plasma sample. The AuNPs-CysA-GA provides a large surface area for the effective immobilization of CEA antibody, as well as it ascertains the bioactivity and stability of immobilized CEA antigens. Biotinylated-anti-CEA antibody (Ab1) was immobilized on the surface of glassy carbon electrode (GCE) modified AuNPs-CysA-GA. Also, secondary antibody (HRP-Ab2) was costed immobilized to complete the sandwich part of immunosensor. Field emission scanning electron microscope (FE-SEM and EDS), was employed to monitor the sensor fabrication procedure. The immunosensor was used for the detection of CEA using differential pulse voltammetry (DPVs) technique. The proposed interface led to enhancement of accessible surface area for immobilizing high amount of anti-CEA antibody, increasing electrical conductivity, boosting stability, and biocompatibility. Finally, the low limit of quantitation (LLOQ) of the proposed immunosensor was obtained as 7 ng/mL with the linear range of 0.001-5 μg/L. The proposed immunoassay was successfully applied for the monitoring of the CEA in unprocessed human plasma samples. Obtained results paved that the proposed bioassay can be used as a novel bioassay for the clinical diagnosis of cancer based on CEA monitoring.

Unravelling the Aptamer-Analyte Interaction Dynamics through Fluorescence Quenching in Graphene Quantum Dots (GQDs) Based Homogeneous Assays

Graphene quantum dots (GQDs) are used here as a biosensing platform for the recognition of the major food contaminant ochratoxin A (OTA), with a fluorescently labelled DNA aptamer (FAM OTA aptamer) functioning as the biorecognition element. The detection principle lies in the formation of noncovalent interactions between the FAM OTA aptamer and the GQD surface, and the consequent fluorescence quenching. The further change in the fluorescence signal, induced by the formation of the FAM OTA Aptamer/OTA conjugate during the detection step, could then be correlated to the presence and concentration of the target analyte. Upon tuning the concentration of GQDs, a switch in the biorecognition mechanism occurred. Specifically, while a lower GQD concentration (0.060 mg/mL) resulted in a restoration of the fluorescence intensity upon incubation with OTA, a higher GQD concentration (0.150 mg/mL) provided a further quenching of the final fluorescence intensity. Upon further calibration study, it was discovered that the latter mechanism provided a better option in terms of linearity of response, detection limit and selectivity.

A fluorometric method for aptamer-based simultaneous determination of two kinds of the fusarium mycotoxins zearalenone and fumonisin B1 making use of gold nanorods and upconversion nanoparticles

An aptamer-based assay for the determination of two different kinds of fusarium mycotoxins, i.e., zearalenone (ZEN) and fumonisin B₁ (FB₁), is presented. Based on the inner filter effect (IFE) strategy, the contents of ZEN and FB₁ can be simultaneously quantified. It is making use of 65-nm gold nanorods (AuNRs), 20-nm upconversion nanoparticles (UCNPs), fluorescence dyes, and DNA sequences. In the absence of ZEN and FB₁, the UCNPs and AuNRs associate through DNA sequences. Due to IFE effect, weak fluorescence signals are collected. In the presence of ZEN or FB₁, UCNPs and AuNRs become unstable and partially separate from each other. This results in the recovery of fluorescence signals. Under 980-nm laser excitation, the logarithmic values of fluorescence signal intensities at 606 nm and 753 nm gradually increase with the concentration of ZEN and FB₁ in the ranges 0.05-100 μg L^-1 (the coefficient of determination is 0.997) and 0.01-100 ng L^-1 (the coefficient of determination is 0.986), respectively. The limits of detection (LOD) of the fabricated assay for ZEN and FB1 are 0.01 μg L^-1 and 0.003 ng L^-1, respectively. The proposed method has a high selectivity over other competitive mycotoxins, including aflatoxin B1, ochratoxin A, patulin and ochratoxin B. The applicability of the assay was evaluated in the determination of ZEN and FB1 contents in spiked corn samples. The average recoveries ranged from 89.9 to 106.6%. This result confirms the practicality of this method. Graphical abstract Schematic representation of an aptamer-based fluorometric method for simultaneous determination of two kinds of the fusarium mycotoxins zearalenone and fumonisin B₁.

Engineering Multivalence Aptamer Probes for Amplified and Label-Free Detection of Antibiotics in Aquatic Products

Excessive use of antibiotics in aquatic products is a serious problem for food safety and human health, and on-site detection of antibiotics is highly demanded. Herein, we proposed multivalence aptamer probes, allowing sensitive, label-free, and homogeneous detection of antibiotics in different aquatic products. Compared to commonly used aptamers, multivalence aptamer probes can provide multiple binding sites and a higher affinity for target molecules, and the iterative binding on different binding sites contributes to an amplified recognition effect, sharply increasing the response and sensitivity of aptamer probes. The 2-valence aptamer probes conferred a limit of detection of 0.097 nM for kanamycin detection, where it is estimated that their sensitivity is enhanced 12 times compared to 1-valence aptamer probes. Meanwhile, multivalence aptamer probes allowed us to specifically identify kanamycin among other antibiotics. It could detect kanamycin residual in aquatic products including river eel and puffer fish, as well as tap water with high precision. A multivalence design strategy of aptamer probes would significantly improve the detection performance of aptamers, facilitating the translation of aptamer for food safety control.

Self-Polymerized Dopamine-Decorated Au NPs and Coordinated with Fe-MOF as a Dual Binding Sites and Dual Signal-Amplifying Electrochemical Aptasensor for the Detection of CEA

Fabrication of functional electrochemical biosensor is a hot topic; however, precise and sensitive cancer detection in early clinical diagnosis is still a great challenge. Continuous efforts have been devoted to explore functional materials for this issue. In this work, we developed a dual binding sites and dual signal-amplifying electrochemical aptasensor of self-polymerized dopamine-decorated Au and coordinated with Fe-MOF (Au@PDA@Fe-MOF) for the detection of carcinoembryonic antigen (CEA). Remarkably, Au@PDA@Fe-MOF features high sensitivity, multiple active sites, good biocompatibility, and excellent selectivity, which is attributed to abundant -COOH in porous Fe-MOF and unsaturated Fe³⁺ sites on the surface of Fe-MOF as the active binding sites grafting more NH₂-functionalized CEA-specific aptamer and redox PDA and Fe-MOF accelerating the movement of electrons for dual signal amplifying. Meanwhile, the electrochemical aptasensor shows favorable repeatability with 1.82% relative standard deviation (RSD) under five independent aptasensors and strong stability with only 3.3% degradation after 12 days of storage. In addition, the aptasensor has wide CEA detection range from 1 fg mL^-1 to 1 μg mL^-1 with a low detection limit of 0.33 fg mL^-1 (S/N = 3). Furthermore, the aptasensor is feasible for accurate and quantitative detection of CEA in serum samples with RSD below 2.32%. The satisfying results demonstrate promising applications of the CEA aptasensor in practical sample analysis and lay an important foundation for other biomarker detection in early clinical diagnosis.

Target-Driven Cascade-Amplified Release of Loads from DNA-Gated Metal-Organic Frameworks for Electrochemical Detection of Cancer Biomarker

In this paper, a label-free and stimuli-responsive electrochemical biosensing platform was fabricated based on target-driven load release from DNA-gated metal-organic frameworks (MOFs) with cascade amplification. By using MOFs (UiO-66-NH₂) as a nanocarrier of electroactive molecules (methylene blue; MB) and the programmably assembled DNA acted as the gatekeeper, the biofunctionalized MOFs (MB@DNA/MOFs) were not only used as an amplified signal label but also worked as three-dimensional tracks for biosensing. In the presence of a target, the nicking endonuclease cleavage process was triggered, leading to the generation of two strands (S1 and S2). Both S1 and S2 act as stimuli to participate in the strand displacement reaction on the MB@DNA/MOFs, which caused the unlocking of the pore to release MB, resulting in the decrease of the signal. Using carcinoembryonic antigen (CEA) as a model target, the cascade-amplified biosensor presented good performance for CEA detection, ranging from 50 fg/mL to 10 ng/mL with a detection limit of 16 fg/mL. The stimuli-responsive DNA-gated MOF-based electrochemical platform exhibited three-dimensional biosensing tracks with rational utilization of the cascade amplification, providing an effective method for cancer biomarker detection.

Aptamer-based biosensor for detecting carcinoembryonic antigen

Carcinoembryonic antigen (CEA), as one of the common tumor markers, is a human glycoprotein involved in cell adhesion and is expressed during human fetal development. Since the birth of human, CEA expression is largely inhibited, with only low levels in the plasma of healthy adults. Generally, CEA will overexpressed in many cancers, including gastric, breast, ovarian, lung, and pancreatic cancers, especially colorectal cancer. As one of the important tumor markers, the detection of CEA has great significance in differential diagnosis, condition monitoring and therapeutic evaluation of diseases. Conventional CEA testing typically uses immunoassay methods. However, immunoassay methods require complex and expensive instruments and professional personnel to operate. Moreover, radioactive element may cause certain damage to the human body, which limits their wide application. In the past few years, biosensors, especially aptamer-based biosensors, have attracted extensive attention due to their high sensitivity, good selectivity, high accuracy, fast response and low cost. This review briefly classifies and describes the advance in optical and electrochemical aptamer biosensors for CEA detection, also explains and compares their advantages and disadvantages.

A photoelectrochemical aptasensor for the detection of 17β-estradiol based on In2S3 and CdS co-sensitized cerium doped TiO2

In₂S₃ and CdS co-sensitized Ce doped TiO₂ optimized the transmission path of electrons.

One-step surfactant-free controllable synthesis and tunable up-conversion/down-shifting white light emissions of Sr2YF7 crystals doped with Ln3+ ions

In this work, uniform and monodisperse Sr₂YF₇ spheres were successfully synthesized via a facile one-step hydrothermal route without employing any surfactant.

Photoelectrochemical detection of circulating tumor cells based on aptamer conjugated Cu2O as signal probe

In this work, a sensitive and reliable photoelectrochemical (PEC) biosensor was proposed based on hexagonal carbon nitride tubes (HCNT) as photoactive material for detection of circulating tumor cells (CTCs). Magnetic Fe₃O₄ nanospheres (MNs) and Cu₂O nanoparticles (Cu₂O NPs) were utilized for highly efficient magnetic capture of CTCs and for signal amplification, respectively. First, anti-epithelial cell adhesion molecule (EpCAM) antibody was linked onto MNs for capture and enrichment of CTCs. With the captured MCF-7 coated onto the electrode, the photocurrent intensity of HCNT was decreased due to the steric hindrance derived from MCF-7. Then, when the Cu₂O-aptamer probe was bound onto the CTC surface, the photocurrent intensity was further decreased because Cu₂O NPs competed with HCNT for absorption of exciting light and the aptamer molecules increased the steric hindrance, which leads to significantly decreased photocurrent response, thus realizing dual signal amplification. Using the breast cancer cell MCF-7 as a model, the proposed PEC biosensor displays good performances with a linear range from 3 to 3000 cell mL^-1 and limit of detection down to 1 cell mL^-1. The HCNT-based PEC biosensor shows good performance for detection of CTCs, which may have potential applications in cancer diagnostics and therapeutics.

Bulk/Surface Defects Engineered TiO2 Nanotube Photonic Crystals Coupled with Plasmonic Gold Nanoparticles for Effective in Vivo Near-Infrared Light Photoelectrochemical Detection

Photoelectrochemical (PEC) techniques are of fundamental and practical importance, and they have been widely used for solar energy conversion and experimental protection. Besides these important applications, an emerging and fast developing PEC application of PEC bioanalysis is receiving more attention from both academic and clinic communities. However, the typical PEC biosensing is still limited under illumination of ultraviolet and visible (UV/vis) light, which hampers its in vivo detection in deep tissues. Expanding the optical absorption wavelength of photoelectrodes from the UV/vis light region into the near-infrared (NIR) light region is highly desirable due to its deep tissue penetrability and minimal invasiveness for organisms, but the exploration of a facile strategy to implement efficient NIR absorption with biocompatible materials is still a big challenge. Herein, under the guidance of theorical calculations, we propose a strategy through modulation of bulk/surface defects and decoration of Au nanoparticles on TiO₂ nanotube photonic crystals to implement efficient NIR response and thus successfully realize sensitive and selective PEC detection of antibiotics in real bio- and experimental-samples under NIR illumination. In addition, we first implement the in vivo PEC detection under illumination of NIR light. We have faith that this new NIR photoelectric responsive strategy will provide a broad platform for detection of life-related biomolecules in deep tissues or even in vivo for real-time measurement and shed light on the intrinsic connections between biomarkers and clinical diseases.

In Situ Generated Plasmonic Silver Nanoparticle-Sensitized Amorphous Titanium Dioxide for Ultrasensitive Photoelectrochemical Sensing of Formaldehyde

Trace concentration of formaldehyde can damage human health and environment. Consequently, it is of great significance to develop an ultrasensitive sensor for its determination. Herein, an ingenious and efficient photoelectrochemical sensor for formaldehyde was constructed by amorphous TiO₂ hollow spheres incorporated with Ag⁺ ions, which were brought about by silica template etching and then the exchange of Ag⁺/Na⁺ ions. The amorphous TiO₂ acted the dual role of Ag⁺ ion probe carriers and photoelectric materials. Upon exposure to the increased concentration of formaldehyde, the Ag nanoparticles were produced in situ, and photocurrent amplification was then achieved in a proportional manner. It is attributed to the injection of hot electrons from plasmonic Ag nanoparticles into the conduction band of amorphous titanium dioxide and therefore enhanced the photocurrent. The linear relationship between 1 and 400 pmol L^-1 resulted from the enhanced photocurrent and increased concentration of formaldehyde, and the detection limit was 0.4 pmol L^-1. Benefiting from an in situ and unique sensitization strategy, this photoelectrochemical sensor exhibited many advantages such as sensitivity, selectivity, cost-effectiveness, convenience of fabrication, low power consumption, and stability.

Dual-Acceptor-Based Upconversion Luminescence Nanosensor with Enhanced Quenching Efficiency for in Situ Imaging and Quantification of MicroRNA in Living Cells

Upconversion nanoparticles (UCNPs) have become competitive materials for bioanalysis, bioimaging, and early diagnosis of diseases, especially cancers. However, traditional upconversion luminescence (UCL) nanosensors are often challenged with complicated covalent modification and relatively poor stability. As efficient energy acceptors in the luminescence resonance energy-transfer (LRET) process, organic dyes exhibit unique advantages such as easy modification and stable property. Herein, a simple and universal bioplatform is constructed for in situ imaging and quantitation of intracellular microRNA-21 (miR-21) using dual-acceptor-based upconversion nanoprobes with enhanced quenching efficiency. In this assay, UCNPs with core-shell structures are synthesized, in which the emitting ions are confined in the shell to take the energy donors and acceptors in close proximity. The complementary DNA (cDNA) that can specifically recognize target miR-21 is labeled with organic dyes TAMRA and black hole quencher as dual acceptors and easily assembled on UCNPs via electrostatic adsorption. Compared with only one acceptor for LRET, two dyes quench more luminescence of UCNPs (>60%), which thus reduce the background and improve the sensitivity. With the enhanced quenching efficiency and simple assembly process, the proposed system is readily applied to in situ imaging of miR-21 in different cancer cells, which further achieves quantification of miR-21 in MCF-7 cells. Therefore, our proposed dual-acceptor-based upconversion nanoplatform opens up new opportunities for sensitive analysis of miRNA and provides potential applications in biomedical and clinical research.

Affinity-Based Detection of Biomolecules Using Photo-Electrochemical Readout

Detection and quantification of biologically-relevant analytes using handheld platforms are important for point-of-care diagnostics, real-time health monitoring, and treatment monitoring. Among the various signal transduction methods used in portable biosensors, photoelectrochemcial (PEC) readout has emerged as a promising approach due to its low limit-of-detection and high sensitivity. For this readout method to be applicable to analyzing native samples, performance requirements beyond sensitivity such as specificity, stability, and ease of operation are critical. These performance requirements are governed by the properties of the photoactive materials and signal transduction mechanisms that are used in PEC biosensing. In this review, we categorize PEC biosensors into five areas based on their signal transduction strategy: (a) introduction of photoactive species, (b) generation of electron/hole donors, (c) use of steric hinderance, (d) in situ induction of light, and (e) resonance energy transfer. We discuss the combination of strengths and weaknesses that these signal transduction systems and their material building blocks offer by reviewing the recent progress in this area. Developing the appropriate PEC biosensor starts with defining the application case followed by choosing the materials and signal transduction strategies that meet the application-based specifications.

Facile, Rapid, and Low-Cost Electrophoresis Titration of Thrombin by Aptamer-Linked Magnetic Nanoparticles and a Redox Boundary Chip

An aptamer-linked assay of a target biomarker (e.g., thrombin) is facing the challenges of long-term run, complex performance, and expensive instrument, unfitting clinical diagnosis in resource-limited areas. Herein, a facile chip electrophoresis titration (ET) model was proposed for rapid, portable, and low-cost assay of thrombin via aptamer-linked magnetic nanoparticles (MNPs), redox boundary (RB), and horseradish peroxidase (HRP). In the electrophoresis titration-redox boundary (ET-RB) model, thrombin was chosen as a model biomarker, which could be captured within 15 min by MNP-aptamer 1 and HRP-aptamer 2, forming a sandwich complex of (MNP-aptamer 1)-thrombin-(HRP-aptamer 2). After MNP separation and chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) within 10 min, an ET-RB run could be completed within 5 min based on the reaction between a 3,3',5,5'-tetramethylbenzidine radical cation (TMB^•+) and l-ascorbic acid in the ET channel. The systemic experiments based on the ET-RB method revealed that the sandwich complex could be formed and the thrombin content could be assayed via an ET-RB chip, demonstrating the developed model and method. In particular, the ET-RB method had the evident merits of simplicity, rapidity (less than 30 min), and low cost as well as portability and visuality, in contrast to the currently used thrombin assay. In addition, the developed method had high selectivity, sensitivity (limit of detection of 0.04 nM), and stability (intraday: 3.26%, interday: 6.07%) as well as good recovery (urine: 97-102%, serum: 94-103%). The developed model and method have potential to the development of a point-of-care testing assay in resource-constrained conditions.

Photoelectrochemical detection of breast cancer biomarker based on hexagonal carbon nitride tubes

Photoelectrochemical (PEC) sensor for sensitive detection of breast cancer biomarker human epidermal growth factor receptor 2 (HER2) utilizing hexagonal carbon nitride tubes (HCNT) as photoactive material is reported. The detection is based on suppression of the PEC current intensity of the sensor. HCNT were synthesized via a facile hydrothermal method with large specific surface area and low electron-hole recombination. Au nanoparticles (AuNPs) were deposited onto the surface of the HCNT, which enhanced the photocurrent intensity of the HCNT by one time. For HER2 detection, peptide specific to HER2 was immobilized on the AuNPs surface for capturing HER2 molecules. The following binding of HER2 with HER2 aptamer and the reaction of phosphate groups on aptamer with molybdate can form molybdophosphate precipitate, which sticks to the surface of HCNT and impedes electron transport. Thus, photocurrent intensity of the sensor was suppressed. Under optimal conditions, the linear relationship between the PEC intensity and the logarithm of HER2 concentration was from 0.5 to 1 ng mL^-1 with low limit of detection (LOD) of 0.08 pg mL^-1. Furthermore, the PEC sensor also displayed capability for detecting HER2 in human serum samples. This PEC sensor signal detection strategy can be easily adapted to other PEC sensors involving DNA and find wide applications. Graphical abstract.

Highly sensitive detection of microcystin-LR under visible light using a self-powered photoelectrochemical aptasensor based on a CoO/Au/g-C3N4 Z-scheme heterojunction

Based on the unique photoelectrochemical properties of a CoO/Au/g-C₃N₄ Z-scheme heterojunction, a self-powered photoelectrochemical (PEC) aptasensor was constructed for the detection of microcystin-leucine arginine (MC-LR). Z-scheme heterojunctions can promote the separation of a photo-induced electron-hole pair, and the surface plasmonic resonance (SPR) of Au nanoparticles can significantly enhance the adsorption of visible light. Importantly, MC-LR molecules were captured by aptamers initially immobilized on the modified electrode due to their high affinity, and then oxidized by the photogenerated holes, which caused an amplified photocurrent signal, allowing the quantitative analysis of MC-LR by measuring the photocurrent intensity change. This PEC MC-LR aptasensor showed high sensitivity and selectivity within a wide linear response range from 0.1 pM to 10 nM and a detection limit of 0.01 pM. The application of this sensor in the analysis of lake water samples provided accurate results with a relative standard deviation (RSD) of 2.6%-4.2%.

Near-Infrared-Responsive Photoelectrochemical Aptasensing Platform Based on Plasmonic Nanoparticle-Decorated Two-Dimensional Photonic Crystals

The photoelectrochemical (PEC) analysis is an emerging and fast developing biosensing technique. However, the in vivo PEC biosensing in deep tissue is seriously hampered because of the shallow penetration depth of ultraviolet and visible light. Expanding the optical absorption wavelength of photoelectrodes from the visible light region into the near-infrared (NIR) light region is highly desirable because of its deep tissue penetrability and minimal invasiveness for organisms, but the exploration of the facile strategy to implement efficient NIR absorption with good biocompatibility is still challenging. Herein, a NIR PEC aptasensor is proposed by coupling plasmonic nanoparticles (NPs) into periodic two-dimensional nanocavity (NC) photonic crystals as photoelectrodes, where the Au NPs are sputtered on a periodic two-dimensional TiO₂ NC photonic crystal substrate to significantly enhance the NIR PEC response and successfully achieve sensitive PEC detection of Hg²⁺ under irradiation of NIR light in blood. We believe that the proposed NIR-responsive Au/TiO₂ NC-based PEC aptasensor will open a new in vivo biosensing model for a series of important biomolecules and pave up an avenue for the practical applications of PEC biosensing in deep tissue or even in organs and brain of the living body.

Emerging ultrafast nucleic acid amplification technologies for next-generation molecular diagnostics

Over the last decade, nucleic acid amplification tests (NAATs) including polymerase chain reaction (PCR) were an indispensable methodology for diagnosing cancers, viral and bacterial infections owing to their high sensitivity and specificity. Because the NAATs can recognize and discriminate even a few copies of nucleic acid (NA) and species-specific NA sequences, NAATs have become the gold standard in a wide range of applications. However, limitations of NAAT approaches have recently become more apparent by reason of their lengthy run time, large reaction volume, and complex protocol. To meet the current demands of clinicians and biomedical researchers, new NAATs have developed to achieve ultrafast sample-to-answer protocols for the point-of-care testing (POCT). In this review, ultrafast NA-POCT platforms are discussed, outlining their NA amplification principles as well as delineating recent advances in ultrafast NAAT applications. The main focus is to provide an overview of NA-POCT platforms in regard to sample preparation of NA, NA amplification, NA detection process, interpretation of the analysis, and evaluation of the platform design. Increasing importance will be given to innovative, ultrafast amplification methods and tools which incorporate artificial intelligence (AI)-associated data analysis processes and mobile-healthcare networks. The future prospects of NA POCT platforms are promising as they allow absolute quantitation of NA in individuals which is essential to precision medicine.

Core-Shell NaHoF4@TiO2 NPs: A Labeling Method to Trace Engineered Nanomaterials of Ubiquitous Elements in the Environment

Understanding the fate and behavior of nanoparticles (NPs) in the natural environment is important to assess their potential risk. Single particle inductively coupled plasma mass spectrometry (spICP-MS) allows for the detection of NPs at extremely low concentrations, but the high natural background of the constituents of many of the most widely utilized nanoscale materials makes accurate quantification of engineered particles challenging. Chemical doping, with a less naturally abundant element, is one approach to address this; however, certain materials with high natural abundance, such as TiO₂ NPs, are notoriously difficult to label and differentiate from natural NPs. Using the low abundance rare earth element Ho as a marker, Ho-bearing core -TiO₂ shell (NaHoF₄@TiO₂) NPs were designed to enable the quantification of engineered TiO₂ NPs in real environmental samples. The NaHoF₄@TiO₂ NPs were synthesized on a large scale (gram), at relatively low temperatures, using a sacrificial Al(OH)₃ template that confines the hydrolysis of TiF₄ within the space surrounding the NaHoF₄ NPs. The resulting NPs consist of a 60 nm NaHoF₄ core and a 5 nm anatase TiO₂ shell, as determined by TEM, STEM-EDX mapping, and spICP-MS. The NPs exhibit excellent detectability by spICP-MS at extremely low concentrations (down to 1 × 10^-3 ng/L) even in complex natural environments with high Ti background.