Enzymatic Biofuel-Cell-Based Self-Powered Biosensor Integrated with DNA Amplification Strategy for Ultrasensitive Detection of Single-Nucleotide Polymorphism

Nanocomposites of boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymers as a novel desorption/ionization matrix for the capture and direct detection of cis-diol-flavonoid compounds coupled with MALDI-TOF-MS

Novel boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymer (Fe₃O₄@MWCNTs@ε-PL@BA) nanocomposites were fabricated and applied as the desorption/ionization matrix for the MALDI-TOF-MS determination of low molecular weight flavonoids. The prepared nanocomposite was systematically characterized by various techniques. Compared to the traditional organic matrix, the proposed Fe₃O₄@MWCNTs@ε-PL@BA matrix has excellent ionization efficiency and low-background noise interference due to the MWCNTs unique electron-phonon interaction and the high introduction density of boronic acid functional groups. Good sensitivity and ultra-high salt tolerance of the Fe₃O₄@MWCNTs@ε-PL@BA-assisted MALDI-TOF-MS were permitted for the determination and quantification of flavonoids in actual samples. Noticeably, the limits of detection (LODs) for the target flavonoids were in the range 17-33 nM. The relative standard deviations (RSDs) of spot-to-spot and sample-to-sample (n = 10) were ≤ 9.8% and ≤ 10.1%, respectively. Furthermore, the wide linear ranges (0.1 - 500 µg/mL) and satisfactory calibration plot coefficients (R² > 0.99) of flavonoids were achieved by MALDI-TOF-MS with the Fe₃O₄@MWCNTs@ε-PL@BA matrix. Good recoveries (92-105.5%) were achieved for the target flavonoids in practical food samples. Hence, the prepared Fe₃O₄@MWCNTs@ε-PL@BA nanocomposites have applications in the selective and efficient capture of target flavonoids active biomolecules coupled with MALDI-TOF-MS determination in actual samples.

Modular Assembly of a Concatenated DNA Circuit for In Vivo Amplified Aptasensing

Probing endogenous molecular profiles in living entities is of fundamental significance to decipher biological functions and exploit novel theranostics. Despite programmable nucleic acid-based aptasensing systems across the breadth of molecular imaging, an aptasensing system enabling in vivo imaging with high sensitivity, accuracy, and adaptability is highly required yet is still in its infancy. Artificial catalytic DNA circuits that can modularly integrate to generate multiple outputs from a single input in an isothermal autonomous manner, have supplemented powerful toolkits for intracellular biosensing research. Herein, a multilayer nonenzymatic catalytic DNA circuits-based aptasensing system is devised for in situ imaging of a bioactive molecule in living mice by assembling branched DNA copolymers with high-molecular-weight and high-signal-gain based on avalanche-mimicking hybridization chain reactions (HCRs). The HCRs aptasensing circuit performs as a general and powerful sensing platform for precise analysis of a series of bioactive molecules due to its inherent rich recognition repertoire and hierarchical reaction accelerations. With tumor-targeting capsule encapsulation, the HCRs aptasensing circuit is specifically delivered into tumor cells and allowed the high-contrast imaging of intracellular adenosine triphosphate in living mice, highlighting its potential for visualizing these clinically important biomolecules and for studying the associated physiological processes.

Interfacial Engineering of a Phase-Controlled Heterojunction for High-Efficiency HER, OER, and ORR Trifunctional Electrocatalysis

The development of low-cost and high-performance electrocatalysts for simultaneously boosting the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is highly crucial but still challenging. Herein, a facile one-step solid-phase polymerization and confined pyrolysis strategy is developed for scalable synthesis of a Fe _x P/Fe₃C-based (x = 1, 2) heterojunction with controllable iron phosphide crystal phases. By effective heterojunction interface regulation, the strong synergic effect between FeP/Fe₃C and N- and P-codoped carbon (NPC) modified the electronic structure, resulting in an excellent electrocatalytic performance for the HER, OER, and ORR synchronously. Typically, the FeP/Fe₃C@NPC catalyst exhibits efficient HER activity with a low overpotential of 10 mA cm^-2 for the HER (97 mV) and OER (440 mV) and a high half-wave potential of 0.87 V for the ORR, as well as excellent stability in alkaline media. Theoretical calculations demonstrated that Fe₃C can promote the activation of water molecules, while FeP is beneficial to the removal of H₂ and the FeP/Fe₃C heterojunction can facilitate both Volmer and Heyrovsky steps in the HER process simultaneously. Moreover, FeP has a stronger inhibitory effect on OH adsorption, revealing that the FeP/Fe₃C heterojunction also shows a better promoting effect for both the OER and ORR, respectively.

Development of label-free fluorescent biosensor for the detection of kanamycin based on aptamer capped metal-organic framework

The abuse of antibiotics has caused serious threat to human health, so it is of great significance to develop a simple and sensitive method for the detection of trace residues of antibiotics in the environment and food. Herein, a novel label-free fluorescent biosensing platform based on the fluorescence change of aptamers-capped zeolitic imidazolate framework-8 (ZIF-8) @ 2,2',2″,2‴-((ethene-1,1,2,2-tetrayltetrakis (benzene-4,1-diyl)) tetrakis (oxy)) tetraacetic acid (TPE) through ATP-assisted competitive coordination reaction was designed for such an end. ZIF-8@TPE/Aptamer (Apt) emits strong fluorescence at 425 nm in HEPES buffer due to the aggregation induced luminescence properties of TPE molecules in confined state. Once kanamycin was added, the conformation of aptamer capped on the surface of ZIF-8@TPE changes because of the specific recognition of kanamycin with aptamer, leading to the collapse of ZIF-8 and release of TPE, accompanied with a dramatic decrease of fluorescence intensity. Under the optimal conditions, a good correlation was obtained between the fluorescence intensity of ZIF-8@TPE/Apt and the concentration of kanamycin ranging from 10 to 10³ ng/mL with a detection limit of 7.3 ng/mL. The satisfactory analytical performance of the assay for kanamycin detection suggests good prospect for its application in food safety analysis.

Versatile Triple-Output Molecular Logic Gate for Cysteine and Silver (I) in Foods and the Environment Based on I-Motif DNA Modulation

DNA-based molecular logic gates have been developed rapidly but most of them have a single output mode. This study is to develop a triple-output label-free fluorescent DNA-based multifunctional molecular logic gate with berberine as a fluorescent signal and a Ag⁺-aptamer as a recognition matrix. The Ag⁺-aptamer has been identified to switch from a random coil to an i-motif structure of C-Ag⁺-C from a Ag⁺-induced responsive conformational change. As a fluorescent probe, berberine is ultrasensitive to the changes of microenvironments, and the binding to i-motif DNA's more rigid structure causes a significant increase in fluorescence, anisotropy, and lifetime. The addition of cysteine to the berberine/C-Ag⁺-C system disintegrates the i-motif DNA structure because of the strong coordination between Ag⁺ and cysteine, and then the triple-output signals are almost retrieved. Given this, a highly sensitive triple-output molecular logic gate for the analyses of Ag⁺ and cysteine is constructed with high specificity. Moreover, this simple and cost-effective molecular logic gate has been applied for the detection of cysteine and Ag⁺ in various real environmental samples including river water, PM_2.5, soil, and food samples with satisfactory recoveries from 89.83 to 106.04%.

A glucose/O2 biofuel cell integrated with an exonuclease-powered DNA walker for self-powered sensing of microRNA

With the aid of an exonuclease-powered DNA walker, the amount of glucose oxidase immobilized on the bioanode can be facilely tailored by varying the concentration of microRNA-141, so a glucose/O₂ biofuel cell is employed as a self-powered sensor for sensitive and selective detection of microRNA-141.

2'-O-Methyl modified guide RNA promotes the single nucleotide polymorphism (SNP) discrimination ability of CRISPR-Cas12a systems

The CRISPR–Cas12a system has been widely applied to genome editing and molecular diagnostics. However, off-target cleavages and false-positive results remain as major concerns in Cas12a practical applications. Herein, we propose a strategy by utilizing the 2′-O-methyl (2′-OMe) modified guide RNA (gRNA) to promote the Cas12a's specificity. Gibbs free energy analysis demonstrates that the 2′-OMe modifications at the 3′-end of gRNA effectively suppress the Cas12a's overall non-specific affinity while maintaining high on-target affinity. For general application illustrations, HBV genotyping and SARS-CoV-2 D614G mutant biosensing platforms are developed to validate the enhanced Cas12a's specificity. Our results indicate that the 2′-OMe modified gRNAs could discriminate single-base mutations with at least two-fold enhanced specificity compared to unmodified gRNAs. Furthermore, we investigate the enhancing mechanisms of the 2′-OMe modified Cas12a systems by molecular docking simulations and the results suggest that the 2′-OMe modifications at the 3′-end of gRNA reduce the Cas12a's binding activity to off-target DNA. This work offers a versatile and universal gRNA design strategy for highly specific Cas12a system development.

This study illustrates that 2′-O-methyl modified gRNAs improve the specificity of the CRISPR–Cas12a system (mg-CRISPR) via suppressing the Cas12a's affinity to off-target DNA and provides an efficient strategy for high-specificity gRNA design.

Photoswitchable Enzymatic Biofuel Cell Based on Fusion Protein with Natural Photoreceptor Vivid

Enzymatic biofuel cells (EBFCs) have increasingly been the subject of research, but the control of the EBFC output remains difficult. In this study, we fuse glucose 6-phosphate dehydrogenase (G6PDH) and diaphorase (DI) with the natural photoreceptor Vivid named "Mag". The output current and power density of EBFCs with the fusion protein exhibit a sensitive and efficient response to blue light. Following optimizations, the power density increases nearly 4-fold from 1.32 to 6.26 μW cm^-2, whereas the current rises from 5.9 to 10.8 μA after 20 min of illumination, dropping back within 30 min under dark conditions.

Development of one-step isothermal methods to detect RNAs using hairpin-loop signal converters and proximity proteolysis reaction

Ribonucleic acids (RNAs) provide valuable information for biological systems and act as important indicators of disease states. RNAs are diverse in size and structure, and various strategies have been proposed for the detection of nucleic acids; however, developing them into point-of-care (POC) tests has been challenging as most of them consist of complex time-consuming steps. Here, we propose a strategy to assay RNAs using a hairpin-loop (HP) converter and proximity proteolysis reaction (PPR). Interaction between the loop part of HP and its target exposes a single strand of nucleotides, which acts as the template for PPR. A pair of protease and zymogen-conjugated nucleic acids associates with the adjacent regions of the template, resulting in an enhanced proteolysis reaction between protease and zymogen. The activated zymogen then generates a color signal through the hydrolysis of a chromogenic substrate. The combination of HP converter and PPR allowed the same pair of protease- and zymogen-nucleic acids to be used for different RNAs. Guidelines were provided for designing HP converters based on computational analyses and experimental characterizations. This strategy using an HP converter and PPR has been successfully applied to develop simple isothermal methods for the detection of various RNAs, including several microRNAs and KRAS mRNA, in the picomolar range in 1 h. The simplicity of designing HP converters and the beneficial properties of PPR as POC tests would enable the development of novel methods to detect RNAs under low-resource conditions.

A universal array platform for ultrasensitive, high-throughput and microvolume detection of heavy metal, nucleic acid and bacteria based on photonic crystals combined with DNA nanomachine

The development of a universal, sensitive, and rapid assay platform to achieve detections of heavy metal, nucleic acid and bacteria is of great significance but it also faces a thorny challenge. Herein, a novel and universal array platform was developed by combining photonic crystals (PCs) and DNA nanomachine. The developed array platform integrated the physical and biological signal amplification ability of PCs and DNA nanomachine, resulting in ultrasensitive detections of Hg²⁺, DNA, and Shigella sonnei with limits of detection (LODs) of 22.1 ppt, 31.6 fM, and 9 CFU/mL, respectively. More importantly, by utilizing a microplate reader as signal output device, the array achieved high-throughput scanning (96 samples/3 min) with only 2 μL loading sample, which is advantageous for the detection of infectious dangerous targets. In addition, the PCs array could be obtained easily and rapidly based on self-assembly of colloidal nanospheres, and the DNA nanomachine was operated with enzyme-free and time-saving features. Benefiting from these merits, the proposed PCs array offered a powerful universal platform for large-scale detection of various analytes in the fields of pollution monitoring, epidemic control, and public health.

Photo-Assisted Robust Anti-Interference Self-Powered Biosensing of MicroRNA Based on Pt-S Bonds and the Inorganic-Organic Hybridization Strategy

Photo-assisted biofuel cell-based self-powered biosensors (PBFC-SPBs) possess the advantages of no need for external power supply, ease of sensing design, and simple instruments. In this work, a robust anti-interference PBFC-SPB for microRNA detection was constructed based on the Pt-S bond and the inorganic-organic hybridization strategy. The organic semiconductor [6,6]-phenyl-C61-butyric acid methylester@anthraquinone (PCBM@anthraquinone) served as an efficient light-harvesting material, and gold nanoparticle@Pt (AuNP@Pt) nanomaterials were immobilized on the surface via electrostatic adsorption for the binding of DNA. Notably, compared to Au-S bonds for DNA immobilization, the Pt-S bond exhibited better anti-interference ability. Ingeniously, cadmium sulfide quantum dots (CdS QDs) were close to the PCBM@anthraquinone substrate electrode to form sensitization structures, which was beneficial to enhance the photocurrent signal. Combining with the laccase-mimicking activity Cu²⁺/carbon nanotubes (Cu²⁺/CNTs) cathode, the PBFC-SPB for microRNA detection was achieved. Once the target existed, the identical sequence complementary microRNA would make DNA2/CdS dissociate and break away from the electrode, leading to a low signal. The linear detection range was 10 fM-100 pM, with the limit of determination of 2.4 fM (3S/N). The as-proposed strategy not only paves a new way for the design of photoelectrochemical biosensing but also opens a door for the construction of robust anti-interference bioassay for microRNA detection.

A target-initiated autocatalytic 3D DNA nanomachine for high-efficiency amplified detection of MicroRNA

Considering the challenges of generating simple and efficient DNA (deoxyribonucleic acid) nanomachines for sensitive bioassays and the great potential of target-induced self-cycling catalytic systems, herein, a novel autocatalytic three-dimensional (3D) DNA nanomachine was constructed based on cross-catalytic hairpin assembly on gold nanoparticles (AuNPs) to generate self-powered efficient cyclic amplification. Typically, the DNA hairpins H1, H2, H3 and H4 were immobilized onto AuNPs first. In the presence of target microRNA-203a, the 3D DNA nanomachines were triggered to activate a series of CHA (catalytic hairpin assembly) reactions. Based on the rational design of the system, the products of the CHA 1 reaction were the trigger of the CHA 2 reaction, which could trigger the CHA 1 reaction in turn, generating an efficient self-powered CHA amplification strategy without adding fuel DNA strands or protein enzymes externally and producing high-efficiency fluorescence signal amplification. More importantly, the proposed autocatalytic 3D DNA nanomachines outperformed conventional 3D DNA nanomachines combined with the single-directional cyclic amplification strategy to maximize the amplification efficiency. This strategy not only achieves high-efficiency analysis of microRNAs (microribonucleic acids) in vitro and intracellularly but also provides a new pathway for highly processive DNA nanomachines, offering a new avenue for bioanalysis and early clinical diagnosis.

Proximity binding induced nucleic acid cascade amplification strategy for ultrasensitive homogeneous detection of PSA

In this work, based on the powerful cycle amplification cascades of proximity hybridization-induced hybridization chain reaction and catalyzed hairpin assembly, we engineered a nonenzymatic and ultrasensitive method which combined the Mg²⁺-DNAzyme recycling signal amplification for the analysis of the human prostate specific antigen. Herein, we adopted PSA-conjugates as triggers in the self-assembly process of two hairpin DNAs (H1, H2) into the products of the CHA which could activate the HCR to induce repeated hybridization. And both ends of each adjacent sequence of the HCR products could form a unit of Mg²⁺-DNAzyme which in presence of cofactor Mg²⁺ could recognize and cyclically cleave the hairpin probes in the solution and thus generate observably enhanced fluorescent signal. Benefit from the nucleic acid circuit amplification strategy, PSA of concentration low to 0.73 pg mL^-1 was detected in this system. This homogeneous sensing method in solution avoid the use of the sophisticated equipment and complex operation, as well as addition of artificial enzyme, thus greatly reducing the constraints and complexity of experimental conditions. Moreover, considering most protein biomarkers in serum don't have their corresponding aptamers, this sensing method provide a general sensing approach for homogeneous sensitive detection of these important protein biomarkers which transfer rough antigen-antibody interactivity to smart signal amplification sensing strategies, thus exhibiting a remarkable prospect in clinical application.

A high-specificity flap probe-based isothermal nucleic acid amplification method based on recombinant FEN1-Bst DNA polymerase

The COVID-19 pandemic has unfortunately demonstrated how easily infectious diseases can spread and harm human life and society. As of writing, pandemic has now been on-going for more than one year. There is an urgent need for new nucleic acid-based methods that can be used to diagnose pathogens early, quickly, and accurately to effectively impede the spread of infections and gain control of epidemics. We developed a flap probe-based isothermal nucleic acid amplification method that is triggered by recombinant FEN1-Bst DNA polymerase, which-through enzymatic engineering-has both DNA synthesis, strand displacement and cleavage functions. This novel method offers a simpler and more specific probe-primer pair than those of other isothermal amplifications. We tested the method's ability to detect SARS-CoV-2 (both ORF1ab and N genes), rotavirus, and Chlamydia trachomatis. The limits of detection were 10 copies/μL for rotavirus, C. trachomatis, and SARS-CoV-2 N gene, and 100 copies/μL for SARS-CoV-2 ORF1ab gene. There were no cross-reactions among 11 other common pathogens with characteristics similar to those of the test target, and the method showed 100% sensitivity and 100% specificity in clinical comparisons with RT-PCR testing. In addition to real-time detection, the endpoint could be displayed under a transilluminator, which is a convenient reporting method for point-of-care test settings. Therefore, this novel nucleic acid senor has great potential for use in clinical diagnostics, epidemic prevention, and epidemic control.

Solid-Phase Primer Elongation Using Biotinylated dNTPs for the Detection of a Single Nucleotide Polymorphism from a Fingerprick Blood Sample

Isothermal recombinase polymerase amplification-based solid-phase primer extension is used for the optical detection of a hypertrophic cardiomyopathy associated single nucleotide polymorphism (SNP) in a fingerprick blood sample. The assay exploits four thiolated primers which have the same sequences with the exception of the 3'-terminal base. Target DNA containing the SNP site hybridizes to all four of the immobilized probes, with primer extension only taking place from the primer containing the terminal base that is complementary to the SNP under interrogation. Biotinylated deoxynucleotide triphosphates are used in the primer extension, allowing postextension addition of streptavidin-poly-horseradish peroxidase to bind to the incorporated biotinylated dNTPs. The signal generated following substrate addition can then be measured optically. The percentage of biotinylated dNTPs and the duration of primer extension is optimized and the system applied to the identification of a SNP in a fingerprick blood sample. A methodology of thermal lysis using a 1 in 5 dilution of the fingerprick blood sample prior to application of 95 °C for 30 s is used to extract genomic DNA, which is directly used as a template for solid-phase primer extension on microtiter plates, followed by optical detection. The SNP in the fingerprick sample was identified and its identity corroborated using ion torrent next generation sequencing. Ongoing work is focused on extension to the multiplexed detection of SNPs in fingerprick and other biological samples.

Dual-signal amplification electrochemical sensing for the sensitive detection of uranyl ion based on gold nanoparticles and hybridization chain reaction-assisted synthesis of silver nanoclusters

Herein, a dual-signal amplification electrochemical sensing has been proposed for the ultrasensitive detection of uranyl ions (UO₂²⁺) by integration of gold nanoparticles (AuNPs) and hybridization chain reaction (HCR)-assisted synthesis of silver nanoclusters (AgNCs). In this sensing platform, AuNPs are used as an ideal signal amplification carrier, aiming at increasing the loads of UO₂²⁺-specific DNAzyme on the gold electrode. In the presence of UO₂²⁺, UO₂²⁺-specific DNAzyme can be activated, leading to the cleavage of substrate strands (S-DNA). Then, HCR is triggered to produce long dsDNA through hybridization the probe with the ssDNA on the electrode surface. As a result, an amplified electrochemical response can be detected by inserting a large amount of AgNCs generated in situ using dsDNA as template. Featured with amplification efficiency, good specificity and high sensitivity, the strategy could quantitatively detect UO₂²⁺ down to 6.2 pM with a linear calibration range from 20 pM to 5000 pM. The proposed sensing platform has been also successfully demonstrated the practical application of detecting UO₂²⁺, indicating that the developed method has the potential applications and can open up a new avenue for highly sensitive detection of UO₂²⁺ in environmental monitoring.

Advances in Nanomaterials-Based Electrochemical Biosensors for Foodborne Pathogen Detection

Electrochemical biosensors utilizing nanomaterials have received widespread attention in pathogen detection and monitoring. Here, the potential of different nanomaterials and electrochemical technologies is reviewed for the development of novel diagnostic devices for the detection of foodborne pathogens and their biomarkers. The overview covers basic electrochemical methods and means for electrode functionalization, utilization of nanomaterials that include quantum dots, gold, silver and magnetic nanoparticles, carbon nanomaterials (carbon and graphene quantum dots, carbon nanotubes, graphene and reduced graphene oxide, graphene nanoplatelets, laser-induced graphene), metal oxides (nanoparticles, 2D and 3D nanostructures) and other 2D nanomaterials. Moreover, the current and future landscape of synergic effects of nanocomposites combining different nanomaterials is provided to illustrate how the limitations of traditional technologies can be overcome to design rapid, ultrasensitive, specific and affordable biosensors.

Ultrasensitive colorimetric strategy for Hg2+ detection based on T-Hg2+-T configuration and target recycling amplification

A novelty aptasensor for ultrasensitive detection of Hg²⁺ is developed, exploiting the combination of plasmonic properties of gold nanoparticles (AuNPs) and exonuclease III (Exo III)-assisted target recycling for signal amplification. In the presence of Hg²⁺, a DNA duplex can be formed due to the strong coordination of Hg²⁺ and T bases of single-stranded DNA (ssDNA) probe. Exo III digests the DNA duplex from the 3' to 5' direction, resulting in the releasing of Hg²⁺. Then, the released Hg²⁺ binds with another ssDNA probe through T-Hg²⁺-T coordination. After Exo III-assisted Hg²⁺ cycles, numerous ssDNA probes are exhausted, which promotes poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation, leading to an obvious color change and aggregation-induced plasmon red shift of AuNPs (from 520 to 610 nm). Therefore, this biosensor is ultrasensitive, which is applicable to the detection of trace level of Hg²⁺ with a linear range from 5 pM to 0.6 nM and an ultralow detection limit of 0.2 pM. Furthermore, it enables visual detection of Hg²⁺ as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg²⁺ in sea water samples with good recovery.

Biofuel Cell-Driven Robust Electrochemiluminescence Biosensing Platform

Electrochemiluminescence (ECL) is one powerful tool in the sensing field, in which the electrochemical workstation is necessary to achieve the electrical/optical signal conversion in the presence of luminescent agents. By contrast, biofuel cells (BFCs) can also provide electricity from renewable biofuels under moderate conditions. More importantly, BFCs with the features of adjustable voltage output and excellent compatibility would well meet the requirement of working voltages for different ECL devices. However, to the best of our knowledge, the BFC-driven luminous system has not been reported. In this work, we constructed, for the first time, a BFC-driven ECL system with fast and stable signal outputs. To demonstrate the proof-of-concept of the BFC-ECL system, the sensitive and selective detection of histidine was achieved, exhibiting great potential among point-of-care diagnoses in remote regions. Overall, this work not only paves a new way for the conversion of chemical energy, electrical energy, and luminous system but also explores the new application of BFC.

A photoelectrochemical self-powered sensor for the detection of sarcosine based on NiO NSs/PbS/Au NPs as photocathodic material

In this study, lead(II) sulfide (PbS) nanocrystals were modified on nickel(II)oxide nanosheets (NiO NSs) via the chemical bath method. Afterwards, Au nanoparticles (NPs) were also modified successfully. A photoelectrochemical (PEC) self-powered platform for detecting sarcosine with high PEC activity was constructed. The capacity of NiO NSs to be loaded with other sensitizing materials was mainly attributed to its porous structure and large specific surface area. Under optimum conditions, the constructed PEC self-powered cathodic sensor for detecting sarcosine exhibited a linear range in 5.0 × 10^-8-5.0 × 10^-2 mol/L with a detection limit (LOD) of 1.7 × 10^-8 mol/L. The biosensor demonstrated good reproducibility, acceptable stability and high specificity, thus confirming its potential application in the detection of other similar substances.

Ultrasensitive detection of PCB77 based on Exonuclease III-powered DNA walking machine

In view of the urgent need to determine polychlorinated biphenyls (PCBs) in the environment, we report a simple and sensitive electrochemical aptasensor to detect 3,3',4,4'-tetrachlorobiphenyl (PCB77) based on Exonuclease III-powered Deoxyribonucleic Acid (DNA) walking machine using poly (diallyldimethylammonium chloride) (PDDA), which was functionalized hollow porous graphitic carbon nitride/ Ni-Co hollow nanoboxes/ Au-Pd-Pt nanoflowers composite material. Upon the addition of PCB77, the specific binding between PCB77 and the aptamer (Apt) could trigger the Exo III-assisted cyclic amplification process and release unlocking probes to deblock the Swing arm/Blocker duplex. Finally, the hybridized hairpin 3 (HP3), a short oligonucleotide, was left on the electrode via Exo III digestion of hybridized HP2, and thus a strong methylene blue (MB) signal was obtained. As expected, the proposed aptasensor exhibits exceptional PCB77 detection performances with a very low detection limit of 5.13 pg/L and a wide linear range of 0.01-100 ng/L based on the calibration curve. Moreover, the aptasensor presents a high level of selectivity and stability, with an acceptable degree of reproducibility. The results of this study have indicated that the proposed aptasensor has great potential application prospects, as demonstrated by its successful use in real environmental water samples.

Antibody-powered DNA switches to initiate the hybridization chain reaction for the amplified fluorescence immunoassay

Designing antibody-powered DNA nanodevice switches is crucial and fascinating to perform a variety of functions in response to specific antibodies as regulatory inputs, achieving highly sensitive detection by integration with simple amplified methods. In this work, we report a unique DNA-based conformational switch, powered by a targeted anti-digoxin mouse monoclonal antibody (anti-Dig) as a model, to rationally initiate the hybridization chain reaction (HCR) for enzyme-free signal amplification. As a proof-of-concept, both a fluorophore Cy3-labeled reporter hairpin (RH) in the 3' terminus and a single-stranded helper DNA (HS) were individually hybridized with a recognition single-stranded DNA (RS) modified with Dig hapten, while the unpaired loop of RH was hybridized with the exposed 3'-toehold of HS, isothermally self-assembling an intermediate metastable DNA structure. The introduction of target anti-Dig drove the concurrent conjugation with two tethered Dig haptens, powering the directional switch of this DNA structure into a stable conformation. In this case, the unlocked 3'-stem of RH was implemented to unfold the 5'-stem of the BHQ-2-labeled quench hairpin (QH), rationally initiating the HCR between them by the overlapping complementary hybridization. As a result, numerous pairs of Cy3 and BHQ-2 in the formed long double helix were located in spatial proximity. In response to this, the significant quenching of the fluorescence intensity of Cy3 by BHQ-2 was dependent on the variable concentration of anti-Dig, achieving a highly sensitive quantification down to the picomolar level based on a simplified protocol integrated with enzyme-free amplification.

Recent Advances in Potentiometric Biosensing

Potentiometric biosensors are incredibly versatile tools with budding uses in industry, security, environmental safety, and human health. This mini-review on recent (2018-2020) advances in the field of potentiometric biosensors is intended to give a general overview of the main types of potentiometric biosensors for novices while still providing a brief but thorough summary of the novel advances and trends for experienced practitioners. These trends include the incorporation of nanomaterials, graphene, and novel immobilization materials, as well as a strong push towards miniaturized, flexible, and self-powered devices for in-field or at-home use.

A single nucleotide polymorphism electrochemical sensor based on DNA-functionalized Cd-MOFs-74 as cascade signal amplification probes

An ultrasensitive electrochemical sensor has been constructed for the detection of single nucleotide polymorphisms (SNPs) based on DNA-functionalized Cd-MOFs-74 as cascade signal amplification probe under enzyme-free conditions. Interestingly, the introduction of an auxiliary probe did not disturb the detection of SNP targets, but could bind more Cd-MOFs-74 signal elements to enhance the different pulse voltammetry electrochemical signal 2~3 times as compared to sensing system without auxiliary probe, which obviously improves the sensitivity of the proposed sensor. Experimental results taking p53 tumor suppressor gene as SNP model demonstrated that the proposed method can be employed to sensitively and selectively detect target p53 gene fragment with a linear response ranging from 0.01 to 30 pmol/L (detection limit of 6.3 fmol/L) under enzyme-free conditions. Utilizing this strategy, the ultrasensitive SNP electrochemical sensor is a promising tool for the determination  of SNPs in biomedicine. Graphical Abstract.

Novel label-free fluorescence aptasensor for chloramphenicol detection based on a DNA four-arm junction-assisted signal amplification strategy

A novel label-free fluorescence aptasensor was established for chloramphenicol (CAP) detection by DNA four-arm junction-assisted target recycling and SYBR Green I dye-aided fluorescence-signal amplification. The CAP aptamer was hybridized to its complementary strand (primer) to form a double-stranded primer/aptamer complex. In the presence of CAP, aptamers can specifically bind with CAP to dissociate primers, which can trigger the self-assembly of four hairpins to continuously generate DNA four-arm junctions. After digesting the excess hairpins using T7 exonuclease, SYBR Green I was inserted into the base pair-rich DNA four-arm junctions, which led to a significant increase in fluorescence intensity. Under optimal conditions, the developed aptasensor can detect CAP in a linear range of 1.0 pg mL^-1 to 10 ng mL^-1 with a detection limit of 0.72 pg mL^-1. The recovery rates in milk and honey ranged from 90.3% to 106.6%. Thus, the method shows substantial potential for CAP detection in food products.

Photogenerated Hole-Induced Chemical-Chemical Redox Cycling Strategy on a Direct Z-Scheme Bi2S3/Bi2MoO6 Heterostructure Photoelectrode: Toward an Ultrasensitive Photoelectrochemical Immunoassay

To achieve high sensitivity for biomolecule detection in photoelectrochemical (PEC) bioanalysis, the ideal photoelectrode and ingenious signaling mechanism play crucial roles. Herein, the feasibility of the photogenerated hole-induced chemical-chemical redox cycling amplification strategy on a Z-scheme heterostructure photoelectrode was validated, and the strategy toward enhanced multiple signal amplification for advanced PEC immunoassay application was developed. Specifically, a direct Z-scheme Bi₂S₃/Bi₂MoO₆ heterostructure was synthesized via a classic hydrothermal method and served as a photoelectrode for the signal response. Under the illumination, the PEC chemical-chemical redox cycling (PECCC) among 4-aminophenol generated by the enzymatic catalysis from a sandwich immunoassay, ferrocene as a mediator, and tris (2-carboxyethyl) phosphine as a reducing agent was run on the Z-scheme Bi₂S₃/Bi₂MoO₆ heterostructure photoelectrode. Exemplified by interleukin-6 (IL-6) as the target, the applicability of the strategy was studied in a PEC immunoassay. Thanks to the multiple signal amplification originating from the high efficiency of the PECCC redox cycling system, the enzymatic amplification, and the fine performance of the Z-scheme Bi₂S₃/Bi₂MoO₆ heterostructure photoelectrode, the assay for IL-6 exhibits a very low detection limit of 2.0 × 10^-14 g/mL with a linear range from 5.0 × 10^-14 to 1.0 × 10^-8 g/mL. This work first validates the feasibility of the PECCC redox cycling on the Z-scheme heterostructure photoelectrode and the good performance of the strategy in PEC bioanalysis. We envision that it would provide a new prospective for highly sensitive PEC bioanalysis on the basis of a Z-scheme heterostructure.

The dumbbell probe mediated triple cascade signal amplification strategy for sensitive and specific detection of uracil DNA glycosylase activity

Uracil DNA glycosylase (UDG) is a key base excision repair (BER) enzyme and its abnormal expression is nearly relevant to several diseases including cancer. The sensitive detection of UDG activity is beneficial for biomedical studies and clinic diagnosis. In this work, we proposed a dumbbell probe mediated triple cascade signal amplification strategy for sensitive and specific detection of UDG activity. The specially designed dumbbell probe contained two uracil bases, two recognition sites for nicking enzyme and a split sequence of DNAzyme. Unsealed dumbbell probes were first connected into sealed dumbbell probes by T4 DNA ligase, and then the unsealed probes were hydrolyzed by exonuclease to ensure the purity of probes. Under the influence of UDG, two uracil bases were removed to produce two apyrimidinic (AP) sites, which were subsequently cleaved by Endo.IV. The probes after cleavage acted as primers and templates for double nicking sites strand displacement amplification (SDA) to produce a mass of two products. The products of SDA continued to act as primers and templates for rolling circle amplification (RCA) to produce repeats containing complete DNAzyme sequences. The DNAzyme repeatedly cleaved multiple molecular beacons (MB), resulting in remarkable fluorescence enhancement. Benefiting from the triple cascade signal amplification, the sensitivity was improved and the detection limit was 7.2 × 10^-5 U mL^-1. The method could well distinguish UDG from other interfering enzymes and detect UDG activity in real biological samples, showing good specificity. In addition, this method could be used for screening inhibitors. The above results suggested that the method provided a promising analytical means for UDG related biomedical research and clinic diagnosis.

Hybridization chain reaction and its applications in biosensing

To pursue the sensitive and efficient detection of informative biomolecules for bioanalysis and disease diagnosis, a series of signal amplification techniques have been put forward. Among them, hybridization chain reaction (HCR) is an isothermal and enzyme-free process where the cascade reaction of hybridization events is initiated by a target analyte, yielding a long nicked dsDNA molecule analogous to alternating copolymers. Compared with conventional polymerase chain reaction (PCR) that can proceed only with the aid of polymerases and complicated thermal cycling, HCR has attracted increasing attention because it can occur under mild conditions without using enzymes. As a powerful signal amplification tool, HCR has been employed to construct various simple, sensitive and economic biosensors for detecting nucleic acids, small molecules, cells, and proteins. Moreover, HCR has also been applied to assemble complex nanostructures, some of which even act as the carriers to execute the targeted delivery of anticancer drugs. Recently, HCR has engendered tremendous progress in RNA imaging applications, which can not only achieve endogenous RNA imaging in living cells or even living animals but also implement imaging-guided photodynamic therapy, paving a promising path to promote the development of theranostics. In this review, we begin with the fundamentals of HCR and then focus on summarizing the recent advances in HCR-based biosensors for biosensing and RNA imaging strategies. Further, the challenges and future perspective of HCR-based signal amplification in biosensing and theranostic application are discussed.

When Fluorescent Sensing Meets Electrochemical Amplifying: A Powerful Platform for Gene Detection with High Sensitivity and Specificity

Ultrasensitive and ultraselective detection of the gene requires emergency development to meet the medical demands and infectious disease control. Herein we report a versatile and scalable method based on electrochemical-chemical-cyclic amplification (EC-CA) and fluorescence detection for ultrasensitive gene sensing. The EC-CA is achieved by an electro-Fenton reaction (EFR). The hydroxyl radicals generated at EFR are trapped by terephthalic acid to form highly fluorescent 2-hydroxyterephthalic acid, which can be sensitively detected by a fluorescence spectrophotometer. The method is the first to be able to amplify the signal and reduce the noise simultaneously by using the conventional analytical methods directly. This described method can be used for reliable Fe³⁺ quantification in the range from 0.1 nM to 0.08 mM. The calculated limit of detection (LOD) is 0.02 nM. Then, hepatitis B virus (HBV) and p53 gene were detected by this proposed method through introducing the Fe₃O₄ nanoparticles into the gene hybridization system. The LODs for HBV and p53 gene even topped out at 2.6 pM and 1.7 fM, respectively. We demonstrated that the finally recorded signal was triply amplified through the EC cycle, Fe₃O₄ nanoparticles, and sensitive fluorescence detection. At the same time, the background signal arisen from matrix effects and readout noise was effectively suppressed. This method shows it is simple, convenient, and operational through the detection of Fe³⁺, HBV, and the p53 gene in blood samples, respectively. We believe our method will make a significant, near-term impact on the development of high-sensitivity methods that are versatile and scalable.

Application of Nanotechnology for Sensitive Detection of Low-Abundance Single-Nucleotide Variations in Genomic DNA: A Review

Single-nucleotide polymorphisms (SNPs) are the simplest and most common type of DNA variations in the human genome. This class of attractive genetic markers, along with point mutations, have been associated with the risk of developing a wide range of diseases, including cancer, cardiovascular diseases, autoimmune diseases, and neurodegenerative diseases. Several existing methods to detect SNPs and mutations in body fluids have faced limitations. Therefore, there is a need to focus on developing noninvasive future polymerase chain reaction (PCR)-free tools to detect low-abundant SNPs in such specimens. The detection of small concentrations of SNPs in the presence of a large background of wild-type genes is the biggest hurdle. Hence, the screening and detection of SNPs need efficient and straightforward strategies. Suitable amplification methods are being explored to avoid high-throughput settings and laborious efforts. Therefore, currently, DNA sensing methods are being explored for the ultrasensitive detection of SNPs based on the concept of nanotechnology. Owing to their small size and improved surface area, nanomaterials hold the extensive capacity to be used as biosensors in the genotyping and highly sensitive recognition of single-base mismatch in the presence of incomparable wild-type DNA fragments. Different nanomaterials have been combined with imaging and sensing techniques and amplification methods to facilitate the less time-consuming and easy detection of SNPs in different diseases. This review aims to highlight some of the most recent findings on the aspects of nanotechnology-based SNP sensing methods used for the specific and ultrasensitive detection of low-concentration SNPs and rare mutations.

Oxidase-loaded hydrogels for versatile potentiometric metabolite sensing

Continuous monitoring of biological metabolites of interest necessitates sensors that are robust, versatile, miniaturizable, and reliable. Electrochemical biosensors have dominated the field of biosensors for decades due to their robust and inexpensive nature. Classically, these sensors use amperometric and voltammetric methods as the sensing modality. One of the greatest limitations with these methods is the dependence of the signal (current, i) on the electrode size, which can change with respect to time due to fouling. Here, we present open circuit potential, an electrochemical technique that is relatively insensitive to electrode size, as a reliable alternative to amperometric and voltammetric techniques for monitoring metabolites of interest. The sensor operates by trapping an oxidase enzyme in a chitosan hydrogel. The oxidase enzyme is required for metabolite specificity. When the oxidase enzyme meets its substrate, oxygen is consumed, and hydrogen peroxide is generated. Hydrogen peroxide generation dominates a half reaction at the platinum surface, resulting in a change in potential. Using the above criteria, we demonstrate the efficacy, long lifetime, sensitivity, and ease of fabrication of glucose sensors, and miniaturize the sensors from macro- to microelectrodes. Additionally, we demonstrate the ease with which this platform can be extended to detect other analytes in the form of a galactose sensor. Our results set a foundation for the generalized use of potentiometric sensors for a broad range of metabolites and applications.

A portable signal-on self-powered aptasensor for ultrasensitive detection of sulfadimethoxine based on dual amplification of a capacitor and biphotoelectrodes

A one-compartment photofuel cell with two photoelectrodes was combined with a capacitor to develop a portable self-powered sensor for sulfadimethoxine (SDM) detection. The developed sensor was applied to the assay of SDM in veterinary drug samples with desirable accuracy and precision.

Fiber-crafted biofuel cell bracelet for wearable electronics

Wearable devices that generate power using sweat have garnered much attention in the field of skin electronics. These devices require high performance with a small volume and low production rate of sweat by living organisms. Here we demonstrate a high-power biofuel cell bracelet based on the lactate in human sweat. The biofuel cell was developed by using a lactate oxidase/osmium-based mediator/carbon nanotube fiber for lactate oxidation and a bilirubin oxidase/carbon nanotube fiber for oxygen reduction; the fibers were woven into a hydrophilic supportive textile for sweat storage. The storage textile was sandwiched between a hydrophobic textile for sweat absorption from the skin and a hydrophilic textile for water evaporation to improve sweat collection. The performance of the layered cell was 74 μW at 0.39 V in 20 mM artificial sweat lactate, and its performance was maintained at over 80% for 12 h. Furthermore, we demonstrated a series-connection between anode/cathode fibers by tying them up to wrap the bracelet-type biofuel cell on the wrist. The booster six-cell bracelet generated power at 2.0 V that is sufficient for operating digital wrist watches.

Photo-driven self-powered biosensors for ultrasensitive microRNA detection based on metal-organic framework-controlled release behavior

We developed a "signal-on" self-powered biosensing strategy by taking full advantage of both photoelectrochemical biofuel cells (PBFCs) and metal-organic framework (MOF)-controlled release behavior for ultrasensitive microRNA assay. PBFC-based self-powered sensors have the unique characteristics of non-requirement of external power sources, simple fabrication process, miniature size, good anti-interference ability and low cost. Furthermore, based on the target microRNA-induced release of the electron donor ascorbic acid and the high catalytic ability of the biocathode to catalyse the oxygen reduction reaction, photo-driven self-powered biosensors for ultrasensitive microRNA detection were successfully realized. The as-proposed signal-on biosensor not only provides a simple and effective strategy, but also possesses the merits of a wide dynamic concentration response range and high sensitivity for microRNA detection, with a limit of detection down to 0.16 fM.

Ethanol Biofuel Cells: Hybrid Catalytic Cascades as a Tool for Biosensor Devices

Biofuel cells use chemical reactions and biological catalysts (enzymes or microorganisms) to produce electrical energy, providing clean and renewable energy. Enzymatic biofuel cells (EBFCs) have promising characteristics and potential applications as an alternative energy source for low-power electronic devices. Over the last decade, researchers have focused on enhancing the electrocatalytic activity of biosystems and on increasing energy generation and electronic conductivity. Self-powered biosensors can use EBFCs while eliminating the need for an external power source. This review details improvements in EBFC and catalyst arrangements that will help to achieve complete substrate oxidation and to increase the number of collected electrons. It also describes how analytical techniques can be employed to follow the intermediates between the enzymes within the enzymatic cascade. We aim to demonstrate how a high-performance self-powered sensor design based on EBFCs developed for ethanol detection can be adapted and implemented in power devices for biosensing applications.

A photoelectrochemical biofuel cell based on a TiO2 nanotube array fluorine-doped tin oxide photoanode

Photoelectrochemical biofuel cells can convert light and chemical energy into electrical energy using a dye-sensitized titania (TiO2) fluorine-doped tin oxide photoanode and a platinum-coated fluorine-doped tin oxide cathode. TiO2 of the photoanode serves both as a support for dyes and as an electron-transporting medium, the structure of which can limit electron trapping and charge transporting and then affect the performance of the photoelectrochemical biofuel cells. TiO2 nanotube array films have been shown to enhance the efficiencies of both charge collection and electron injection, and hence a vertically aligned TiO2 nanotube array is investigated as a conductor for the tetrakis(4-carboxyphenyl)porphyrin dye to construct a new two-compartment photoelectrochemical biofuel cell. The photoelectrochemical biofuel cell containing the TiO2 nanotube array photoanode yields a short-circuit (Isc) current of 110 μA and an open-circuit (Voc) potential of 1010 mV. In contrast, the photovoltaic parameters, Isc and Voc of the photoelectrochemical biofuel cell with the mesoporous TiO2 nanocrystal fluorine-doped tin oxide photoanode, are 96.96 μA and 740 mV, respectively. Photovoltaic measurements show that the maximum incident photon-to-collected electron conversion efficiency was 58% at 430 nm through the spectral range (400–800 nm) for the photoelectrochemical biofuel cell with the TiO2 nanotube array fluorine-doped tin oxide photoanode. These results revealed that the TiO2 nanotube array had great potential for the photoelectrochemical biofuel cells.

Allele-specific PCR with a novel data processing method based on difference value for single nucleotide polymorphism genotyping of ALDH2 gene

Single nucleotide polymorphism (SNP) analysis based on allele-specific polymerase chain reaction (AS-PCR) is a relatively effective and economical method compared with other genotyping technologies such as DNA sequencing, DNA hybridization and isothermal amplification strategies. But AS-PCR is limited by its labor-intensive optimization of reaction parameters and time-consuming result assessment. In this study, we put forward a novel idea of data processing to address this problem. SNP analysis was accomplished by AS-PCR with endpoint electrochemical detection. For each sample, two separate reactions were run simultaneously with two sets of allele-specific primers (wild-type primers for W system and mutant primers for M system). We measured their redox current signals on screen-printed electrodes once AS-PCR finished and calculated the difference value of current signals between two systems to determine the genotyping result. Based on the difference value of fluorescent signals, real-time fluorescent PCR was used to study reaction parameters in AS-PCR. With screened parameters, we obtained the genotyping results within 50 min. 36 hair-root samples from volunteers were analyzed by our method and their genotypes of ALDH2 gene (encoding aldehyde dehydrogenase 2) were totally identical with data from commercialized sequencing. Our work first employed difference value between two reaction systems to differentiate allele and provided a novel idea of data processing in AS-PCR method. It is able to promote the quick analysis of SNP in the fields of health monitor, disease precaution, and personalized diagnosis and treatment.

Aggregation-Induced Synergism by Hydrophobic-Driven Self-Assembly of Amphiphilic Oligonucleotides

The evident contradiction between high local-concentration-based substrate reactivity and free-diffusion-based high reaction efficiency remains one of the important challenges in chemistry. Herein, we propose an efficient aggregation-induced synergism through the hydrophobic-driven self-assembly of amphiphilic oligonucleotides to generate high local concentration whereas retaining high reaction efficiency through hydrophobic-based aggregation, which is important for constructing efficient DNA nanomachines for ultrasensitive applications. MicroRNA-155, used as a model, triggered strand displacement amplification of the DNA monomers on the periphery of the 3D DNA nanomachine and generated an amplified fluorescent response for its sensitive assay. The local concentration of substrates was increased by a factor of at least 9.0×10⁵ through hydrophobic-interaction-based self-assembly in comparison with the traditional homogeneous reaction system, achieving high local-concentration-based reactivity and free-diffusion-based enhanced reaction efficiency. As expected, the aggregation-induced synergism by hydrophobic-driven self-assembly of amphiphilic oligonucleotides created excellent properties to generate a 3D DNA nanomachine with potential as an assay for microRNA-155 in cells. Most importantly, this approach can be easily expanded for the bioassay of various biomarkers, such as nucleotides, proteins, and cells, offering a new avenue for simple and efficient applications in bioanalysis and clinical diagnosis.

Anode-Driven Controlled Release of Cathodic Fuel via pH Response for Smart Enzymatic Biofuel Cell

Enzymatic biofuel cells (EBFCs) with or without a membrane to separate the anodic and cathodic compartments generally suffered from high internal resistance or interactive interference, both of which restricted the improvement of their performance. Herein, a smart membrane-less EBFC was engineered based on anode-driven controlled release of cathodic acceptor via pH-responsive metal-organic framework ([Fe(CN)6]3-@ZIF-8) nanocarriers. The glucose anodic oxidation would produce gluconic acid accompanied by the change in pH value from neutral to the acidic case, which could drive the degradation of [Fe(CN)6]3-@ZIF-8 nanocarriers and further realize the controlled release of cathodic acceptor [Fe(CN)6]3-. More importantly, compared with controlled EBFC with or without membrane, the power output of the as-proposed EBFC enhanced at least 700 times due to the seamless electronic communication. Therefore, the ingenious strategy not only realized the successful engineering of the membrane-less EBFC but also provided an appealing idea for constructing smart devices.

A novel self-powered aptasensor for digoxin monitoring based on the dual-photoelectrode membrane/mediator-free photofuel cell

Self-powered sensor is considered as a promising, rapid, portable and miniaturized detection device that can work without external power input. In this work, a novel dual-photoelectrode self-powered aptasensor for digoxin detection was designed on the basis of a photofuel cell (PFC) composed of a black TiO₂ (B-TiO₂) photoanode and a CuBr photocathode in a single-chamber cell. The sensing platform avoided the use of membrane, free mediator, bioactive components and costly metal Pt electrodes. The large inherent bias between the Fermi energy level of B-TiO₂ and that of CuBr improved the electricity output of PFC that the open circuit potential (OCP) and the maximum power density (P_max) reached 0.58 V and 6.78 μW cm^-2 respectively. Based on the excellent output of PFC, digoxin aptamer was immobilized on photoanode as the recognition element to capture digoxin molecules, which realized the high sensitive and selective detection of digoxin. The self-powered aptasensor displayed a broad linear in the range from 10^-12 M to 10^-5 M with a detection limit (3 S/N) of 0.33 pM. This work paved a luciferous way for further rapid, portable, miniaturized and on-site self-powered sensors.

Recent development of biofuel cell based self-powered biosensors

BFC-based SPBs have been used as power sources for other devices and as sensors for detecting toxicity and BOM.

A high-energy sandwich-type self-powered biosensor based on DNA bioconjugates and a nitrogen doped ultra-thin carbon shell

A high-energy self-powered sensing platform for the ultrasensitive detection of proteins is developed based on enzymatic biofuel cells (EBFCs) by using DNA bioconjugate assisted signal amplification.

An Autonomous Nonenzymatic Concatenated DNA Circuit for Amplified Imaging of Intracellular ATP

A robust ATP aptasensor has been successfully constructed for intracellular imaging via the autonomous nonenzymatic cascaded hybridization chain reaction (Ca-HCR) circuit. This compact aptasensor is easily assembled by integrating the sensing module and amplification module, and is furtherly introduced for selective adenosine triphosphate (ATP) assay and for the sensitive tracking of varied ATP expressions in living cells. The ATP-targeting aptamer-encoded sensing module can specifically recognize ATP and release the initiator strand for successively motivating the two-layered HCR (hybridization chain reaction) circuit via the FRET transduction mechanism. The synergistic reaction acceleration of the two HCRs contributes to the high signal gain (amplification efficiency of N²). The whole reaction process was modeled and simulated by MATLAB to deeply explore the underlying molecular reaction mechanism, implying that the cascade HCR is sufficient enough to guarantee the ATP-recognition and amplification processes. The Ca-HCR-amplified aptasensor shows high sensitivity and selectivity for in vitro ATP assay, and can monitor these varied ATP expressions in living cells via intracellular imaging technique. Furthermore, the present aptasensor can be easily extended for monitoring other low-abundance biomarkers, which is especially important for precisely understanding these related biological processes.

An enzyme-free DNA circuit for the amplified detection of Cd2+ based on hairpin probe-mediated toehold binding and branch migration

An enzyme-free DNA circuit was designed for the amplified detection of Cd2+ based on hairpin probe-mediated toehold binding and branch migration. A Cd2+-specific aptamer was used to recognize Cd2+ and a G-quadruplex was used to report the detection signal. The assay is sensitive, with a detection limit of 5 pM.