Pt/Zn-TCPP Nanozyme-Based Flexible Immunoassay for Dual-Mode Pressure-Temperature Monitoring of Low-Abundance Proteins.

Pressure and temperature, as common physical parameters, are important for monitoring human health. In contrast, single-mode monitoring is prone to causing experimental errors. Herein, we innovatively designed a dual-mode flexible sensing platform based on a platinum/zinc-meso-tetrakis(4-carboxyphenyl)porphyrin (Pt/Zn-TCPP) nanozyme for the quantitative monitoring of carcinoembryonic antigen (CEA) in biological fluids with pressure and temperature readouts. The Pt/Zn-TCPP nanozyme with catalytic and photothermal efficiencies was synthesized by means of integrating photosensitizers into porous materials. The flexible sensing system after the antigen-antibody reaction recognized the pressure using a flexible skin-like pressure sensor with a digital multimeter readout, whereas the temperature was acquired via the photoheat conversion system of the Pt/Zn-TCPP nanozyme under 808 nm near-infrared (NIR) irradiation using a portable NIR imaging camera on a smartphone. Meanwhile, the dual-mode flexible sensing system was carried out on a homemade three-dimensional (3D)-printed device. Results revealed that the developed dual-mode immunosensing platform could exhibit good pressure and temperature responses within the dynamic range of 0.5-100 ng mL-1 CEA with the detection limits of 0.24 and 0.13 ng mL-1, respectively. In addition, the pressure and temperature were sensed simultaneously without crosstalk interference. Importantly, the dual-mode flexible immunosensing system can effectively avoid false alarms during the measurement, thus providing great potential for simple and low-cost development for point-of-care testing.

Shaping the Future of the Neurotransmitter Sensor: Tailored CdS Nanostructures for State-of-the-Art Self-Powered Photoelectrochemical Devices.

Semiconductor-based photoelectrochemical (PEC) test protocols offer a viable solution for developing efficient individual health monitoring by converting light and chemical energy into electrical signals. However, slow reaction kinetics and electron-hole complexation at the interface limit their practical application. Here, we reported a triple-engineered CdS nanohierarchical structures (CdS NHs) modification scheme including morphology, defective states, and heterogeneous structure to achieve precise monitoring of the neurotransmitter dopamine (DA) in plasma and noninvasive body fluids. By precisely manipulating the Cd-S precursor, we achieved precise control over ternary CdS NHs and obtained well-defined layered self-assembled CdS NHs through a surface carbon treatment. The integration of defect states and the thin carbon layer effectively established carrier directional transfer pathways, thereby enhancing interface reaction sites and improving the conversion efficiency. The CdS NHs microelectrode fabricated demonstrated a remarkable negative response toward DA, thereby enabling the development of a miniature self-powered PEC device for precise quantification in human saliva. Additionally, the utilization of density functional theory calculations elucidated the structural characteristics of DA and the defect state of CdS, thus establishing crucial theoretical groundwork for optimizing the polymerization process of DA. The present study offers a potential engineering approach for developing high energy conversion efficiency PEC semiconductors as well as proposing a novel concept for designing sensitive testing strategies.

Vanadium-doped metal-organic framework@Znln2S4 core-shell heterojunction-attenuated photoelectrochemical immunoassay.

Considering that cancer has become the second leading cause of death in humans, it is essential to develop an analytical approach that can sensitively detect tumor markers for early detection. We report an attenuated photoelectrochemical (PEC) immunoassay based on the organic-inorganic heterojunction 10MIL-88B(FeV)/ZnIn2S4 (10M88B(FeV)/ZIS) as a photoactive material for monitoring carcinoembryonic antigen (CEA). The 10M88B(FeV)/ZIS heterojunctions have excellent light-harvesting properties and high electrical conductivity, which are attributed to the advantages of both organic and inorganic semiconductors, namely, remarkable photogenerated carrier separation efficiency and long photogenerated carrier lifetime. Horseradish peroxidase (HRP) in the presence of H2O2 can catalyze 3,3'-diaminofenamide (DAB) producing brown precipitates (oxDAB), which is then loaded onto the 10M88B(FeV)/ZIS heterojunction to reduce the photocurrent and enable the quantitative detection of CEA. Under optimal conditions, the photocurrent values of the PEC biosensor are linearly related to the logarithm of the CEA concentrations, ranging from 0.01 ng mL-1 to 100 ng mL-1 with a detection limit (LOD) of 4.0 pg mL-1. Notably, the accuracy of the PEC biosensor is in agreement with that of the human CEA enzyme-linked immunosorbent assay (ELISA) kit.

Foldable paper-based photoelectrochemical biosensor based on etching reaction of CoOOH nanosheets-coated laser-induced PbS/CdS/graphene for sensitive detection of ampicillin.

Timely and rapid detection of antibiotic residues in the environment is conducive to safeguarding human health and promoting an ecological virtuous cycle. A foldable paper-based photoelectrochemical (PEC) sensor was successfully developed for the detection of ampicillin (AMP) based on glutathione/zirconium dioxide hollow nanorods/aptamer (GSH@ZrO2 HS@apt) modified cellulose paper as a reactive zone with laser direct-writing lead sulfide/cadmium sulfide/graphene (PbS/CdS/LIG) as photoelectrode and cobalt hydroxide (CoOOH) as a photoresist material. Initially, AMP was introduced into the paper-based reaction zone as a biogate aptamer, which specifically recognized the target and then left the ZrO2 HS surface, releasing glutathione (GSH) encapsulated inside. Subsequently, the introduction of GSH into the reaction region and etching of CoOOH nanosheets to expose the PbS/CdS/LIG photosensitive material increased photocurrent. Under optimal conditions, the paper-based PEC biosensor showed a linear response to AMP in the range of 5.0 - 2 × 104 pM with a detection limit of 1.36 pM (S/N = 3). In addition, the constructed PEC sensing platform has excellent selectivity, high stability and favorable reproducibility, and can be used to assess AMP residue levels in various real water samples (milk, tap water, river water), indicating its promising application in environmental antibiotic detection.

High-Volumetric Density Atomic Cobalt on Multishell ZnxCd1-xS Boosts Photocatalytic CO2 Reduction.

The volumetric density of the metal atomic site is decisive to the operating efficiency of the photosynthetic nanoreactor, yet its rational design and synthesis remain a grand challenge. Herein, we report a shell-regulating approach to enhance the volumetric density of Co atomic sites onto/into multishell ZnxCd1-xS for greatly improving CO2 photoreduction activity. We first establish a quantitative relation between the number of shell layers, specific surface areas, and volumetric density of atomic sites on multishell ZnxCd1-xS and conclude a positive relation between photosynthetic performance and the number of shell layers. The triple-shell ZnxCd1-xS-Co1 achieves the highest CO yield rate of 7629.7 µmol g-1 h-1, superior to those of the double-shell ZnxCd1-xS-Co1 (5882.2 µmol g-1 h-1) and single-shell ZnxCd1-xS-Co1 (4724.2 µmol g-1 h-1). Density functional theory calculations suggest that high-density Co atomic sites can promote the mobility of photogenerated electrons and enhance the adsorption of Co(bpy)32+ to increase CO2 activation (CO2 → CO2* → COOH* → CO* → CO) via the S-Co-bpy interaction, thereby enhancing the efficiency of photocatalytic CO2 reduction.

A papain-based colorimetric catalytic sensing system for immunoassay detection of carcinoembryonic antigen.

A colorimetric immunoassay was built for determination of carcinoembryonic antigen (CEA) based on papain-based colorimetric catalytic sensing system through the use of glucose oxidase (GOx). In the presence of GOx, glucose was catalytically oxidized to produce H2O2. Through the assistance of papain (as a peroxide mimetic enzyme), the signal came from the oxidative color development of 3,3',5,5'-tetramethylbenzidine (TMB, from colorless to blue) catalyzed by the generated H2O2. Herein, a sandwich-type immunoassay was built based on GOx as labels. As the concentration of CEA increased, more GOx-labeled antibodies specifically associate with target, which leaded to more H2O2 generation. Immediately following this, more TMB were oxidized with the addition of papain. Accordingly, the absorbance increased further. As a result, the concentration of CEA is positively correlated with the change in absorbance of the solution. Under optimal conditions, the CEA concentration was linear in the range of 0.05-20.0 ng/mL, and the limit of detection (LOD) reached 37 pg/mL. The papain-based colorimetric immunoassay also exhibited satisfactory repeatability, stability, and selectivity.

Split-type photoelectrochemical immunoassay for sensitive quantification of carcinoembryonic antigen based on target-induced in situ formation of Z-type heterojunction.

Carcinoembryonic antigen (CEA), a vital biomarker, plays a significant role in the early diagnosis and prognostic estimation of malignant tumors. In this study, a split-type photoelectrochemical immunoassay for the sensitive quantification of CEA has been successfully developed based on the target-induced in situ formation of a Z-type heterojunction. First, gold nanoparticle-decorated ZnIn2S4 (AuNPs/ZnIn2S4) composites were synthesized and used for the fabrication of photoelectrodes. Then, the detection antibody labeled with Ag nanoparticles was formed and applied for the biorecognition of CEA and subsequent liberation of Ag+ ions to induce the in situ formation of Ag2S/AuNPs/ZnIn2S4, a Z-type heterojunction, on the photoelectrode. The Z-type Ag2S/AuNPs/ZnIn2S4 heterojunction with effectively promoted separation of photogenerated charge carriers could lead to a markedly enhanced photocurrent response and highly sensitive quantification of CEA. Moreover, the three-dimensional spatial structure of ZnIn2S4 provides abundant active sites for the reaction and exhibits non-enzymatic properties, which are conducive to the further improvement of the analytical performance of CEA. The developed split-type photoelectrochemical immunoassay with good sensitivity, satisfactory selectivity, reliable stability, wide dynamic linear range (0.01-20 ng mL-1), and low detection limit (7.3 pg mL-1) offers valuable insights into the development of novel PEC biosensing models for the detection of tumor biomarkers and holds potential application value in the field of disease diagnosis.

Excited-State Intramolecular Proton Transfer-Driven Photon-Gating for Photoelectrochemical Sensing of CO-Releasing Molecule-3.

Different from prevalent approaches such as immunological recognition, complementary base pairing, or enzymatic regulation in current photoelectrochemical (PEC) sensing, this study reported an excited-state intramolecular proton transfer (ESIPT)-driven photon-gating PEC sensor. The sensor is developed for the detection of CO-releasing molecule-3 (CORM-3) by modifying an ESIPT-switched organic fluorescent probe molecule (NDAA) onto the surface of a p-type semiconductor (BiOI). The NDAA can be excited and exhibit strong green fluorescence after responding with CORM-3, resulting in an electrode-interface photon competitive absorption effect due to the switch on ESIPT and considerably reducing the photocurrent signal. The experimental results revealed that the as-developed PEC sensor achieved good analytical performance with high selectivity and sensitivity, with a linear range of 0.01-1000 µM and a lower detection limit of 6.5 nM. This work demonstrates the great potential of the organic fluorescent probe molecule family in advancing PEC analysis. It is anticipated that our findings will stimulate the creation of diverse functional probes possessing distinctive characteristics for inventive PEC sensors.

Portable photoelectrochemical immunoassay with micro-electro-mechanical-system for alpha-fetoprotein in hepatocellular carcinoma.

Early detection of cancer has a profound impact on patient survival and treatment outcomes considering high treatment success rates and reduced treatment complexity. Here, we developed a portable photoelectrochemical (PEC) immune platform for sensitive testing of alpha-fetoprotein (AFP) based on Pt nanocluster (Pt NCs) loaded defective-state g-C3N4 photon-electron transducers. The broad forbidden band structure of g-C3N4 was optimized by the nitrogen doping strategy and additional homogeneous porous structure was introduced to further enhance the photon utilization. In addition, the in-situ growth of Pt NCs provided efficient electron transfer catalytic sites for sacrificial agents, which were used to further improve the sensitivity of the sensor. Efficient photoelectric conversion under a hand-held flashlight was determined by the geometry of the transducer and the energy band design, and the portable design of the PEC sensor was realized. The developed sensing platform exhibited a wide linear response range (0.1-50 ng mL-1) and low limit of detection (0.043 ng mL-1) for AFP under optimum conditions. This work provides a new idea for designing portable PEC biosensing platforms to meet the current mainstream POC testing needs.

Precise Tuning of the D-Band Center of Dual-Atomic Enzymes for Catalytic Therapy.

Single-atom nanozyme-based catalytic therapy is of great interest in the field of tumor catalytic therapy; however, their development suffers from the low affinity of nanozymes to the substrates (H2O2 or O2), leading to deficient catalytic activity in the tumor microenvironment. Herein, we report a new strategy for precisely tuning the d-band center of dual-atomic sites to enhance the affinity of metal atomic sites and substrates on a class of edge-rich N-doped porous carbon dual-atomic sites Fe-Mn (Fe1Mn1-NCe) for greatly boosting multiple-enzyme-like catalytic activities. The as-made Fe1Mn1-NCe achieved a much higher catalytic efficiency (Kcat/Km = 4.01 × 105 S-1·M-1) than Fe1-NCe (Kcat/Km = 2.41 × 104 S-1·M-1) with an outstanding stability of over 90% activity retention after 1 year, which is the best among the reported dual-atom nanozymes. Theoretical calculations reveal that the synergetic effect of Mn upshifts the d-band center of Fe from -1.113 to -0.564 eV and enhances the adsorption capacity for the substrate, thus accelerating the dissociation of H2O2 and weakening the O-O bond on O2. We further demonstrated that the superior enzyme-like catalytic activity of Fe1Mn1-NCe combined with photothermal therapy could effectively inhibit tumor growth in vivo, with an inhibition rate of up to 95.74%, which is the highest value among the dual-atom artificial enzyme therapies reported so far.

Surface plasmon resonance-enhanced photoelectrochemical immunoassay with Cu-doped porous Bi2WO6 nanosheets.

The development of rapid screening sensing platforms to improve pre-screening mechanisms in community healthcare is necessary to meet the significant need for portable testing in biomarker diagnostics. Here, we designed a portable smartphone-based photoelectrochemical (PEC) immunoassay for carcinoembryonic antigen (CEA) detection using Cu-doped ultrathin porous Bi2WO6 (CuBWO) nanosheets as the photoactive material. The CuBWO nanosheets exhibit a fast photocurrent response and excellent electrical transmission rate under UV light due to their surface plasmon resonance effect (SPR). The method uses glucose oxidase-labeled secondary antibody as a signal indicator for sandwich-type immune conjugation. In the presence of the target CEA, the electrons and holes generated at the surface of the photo-excited ultrathin porous CuBWO were rapidly consumed by the production of H2O2 from glucose oxidase oxidizing glucose, resulting in a weakened photocurrent signal. The photocurrent intensity increased logarithmically and linearly with increasing CEA concentration (0.02-50 ng mL-1), with a detection limit of 15.0 pg mL-1 (S/N = 3). The system provides a broader idea for inferring the electron-hole transport mechanism in ultrathin porous nanosheet layer materials and developing efficient PEC sensors.

A laser-induced zinc oxide/graphene photoelectrode for a photocurrent-polarity-switching photoelectrochemical biosensor with bipedal DNA walker amplification.

A photocurrent-polarity-switching photoelectrochemical (PEC) biosensor was developed for the ultrasensitive detection of tobramycin (TOB) through bipedal DNA walker amplification with hemin-induced photocurrent-polarity-switching using a laser-induced zinc oxide/graphene (ZnO/LIG) photoelectrode. Specifically, the ZnO/LIG photoelectrode was synthesized in situ by a laser direct writing (LDW) technique. In the presence of TOB, it reacted with HP1 and HP2 and the DNA walker response was activated to form a stable hemin/G-quadruplex. Furthermore, hemin induced a polarity shift in the photocurrent signal. The developed analytical platform exhibited excellent photoelectron transport performance of ZnO/LIG, the signal amplification effect of the DNA walker strategy, and the photocurrent-polarity-switching ability of hemin. Therefore, it demonstrated satisfying photocurrent responses to the target TOB within the working range of 20 nM-1.0 µM at a low detection limit of 5.43 nM. The PEC platform exhibited good stability, reproducibility, sufficient sensitivity and high selectivity for complex experimental samples. Moreover, the photocurrent-polarity-switching PEC biosensor improved the anti-interference ability and avoided false positives or negatives.

Domain-Limited Sub-Nanometer Co Nanoclusters in Defective Nitrogen Doped Carbon Structures for Non-Invasive Drug Monitoring.

In this work, sub-nanometer Co clusters anchored on porous nitrogen-doped carbon (C─N─Co NCs) are successfully prepared by high-temperature annealing and pre-fabricated template strategies for non-invasive sensing of clozapine (CLZ) as an efficient substrate adsorption and electrocatalyst. The introduction of Co sub-nanoclusters (Co NCs) provides enhanced electrochemical performance and better substrate adsorption potential compared to porous and nitrogen-doped carbon structures. Combined with ab initio calculations, it is found that the favorable CLZ catalytic performance with C─N─Co NCs is mainly attributed to possessing a more stable CLZ adsorption structure and lower conversion barriers of CLZ to oxidized state CLZ. An electrochemical sensor for CLZ detection is conceptualized with a wide operating range and high sensitivity, with monitoring capabilities validated in a variety of body fluid environments. Based on the developed CLZ sensing system, the CLZ correlation between blood and saliva and the accuracy of the sensor are investigated by the gold standard method and the rat model of drug administration, paving the way for non-invasive drug monitoring. This work provides new insights into the development of efficient electrocatalysts to enable drug therapy and administration monitoring in personalized healthcare systems.

Bifunctional TiO2 Nanoflower-Induced H4TCBPE Aggregation Enhanced Electrochemiluminescence for an Ultrasensitive Assay of Organophosphorus.

In this work, the aggregation-induced emission ligand 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene (H4TCBPE) was rigidified in the Ti-O network to form novel electrochemiluminescence (ECL) emitter H4TCBPE-TiO2 nanospheres, which acted as an effective ECL emitter to construct an "on-off" ECL biosensor for ultrasensitive detection of malathion (Mal). H4TCBPE-TiO2 exhibited excellent ECL responses due to the Ti-O network that can restrict the intramolecular free motions within H4TCBPE and then reduce the nonradiative relaxation. Moreover, TiO2 can act as an ECL co-reaction accelerator to promote the generation of sulfate radical anion (SO4•-), which interacts with H4TCBPE in the Ti-O network to produce enhanced ECL response. In the presence of Mal, numerous ligated probes (probe 1 to probe 2, P1-P2) were formed and released by copper-free click nucleic acid ligation reaction, which then hybridized with hairpin probe 1 (H1)-modified H4TCBPE-TiO2-based electrode surface. The P1-P2 probes can initiate the target-assisted terminal deoxynucleoside transferase (TdTase) extended reaction to produce long tails of deoxyadenine with abundant biotin, which can load numerous streptavidin-functionalized ferrocenedicarboxylic acid polymer (SA-PFc), causing quenching of the ECL signal. Thus, the ultrasensitive ECL biosensor based on H4TCBPE-TiO2 ECL emitter and click chemistry-actuated TdTase amplification strategy presents a desirable range from 0.001 to 100 ng/mL and a detection limit low to 9.9 fg/mL. Overall, this work has paved an avenue for the development of novel ECL emitters, which has opened up new prospects for ECL biosensing.

Edge-generated N-doped carbon-supported dual-metal active sites for enhancing electrochemical immunoassay.

Development of high-precision human epidermal growth factor receptor 2 (HER2) assay is essential for the early diagnostic and prevention of breast cancer. In this work, an innovative Fe/Mn bimetallic nanozyme at the edge of N-doped carbon defects (FeMn-NCedge) with abundant active sites was prepared through the hydrothermal synthetic method. FeMn-NCedge nanozyme displayed excellent peroxidase-like activity relative to the H2O2-catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) system for generation of the oxidized TMB (oxTMB). As a proof-of-concept application, we constructed an electrochemical immunoassay for the detection of HER2 based on the unique merits of FeMn-NCedge. Initially, a sandwiched immunoreaction was carried out in the microtiter plate coated with monoclonal anti-HER2 capture antibodies using glucose oxidase (GOx)-labeled anti-HER2 as detection antibody. The carried GOx could catalyze glucose to produce H2O2, thus resulting in the formation of oxTMB with the assistance of TMB and FeMn-NCedge nanozyme. The produced oxTMB could be determined on the electrode by the chronoamperometry at an applied potential of +10 mV. Experimental results revealed that the steady-state current increased with the increasing HER2 concentration in the sample, and gave a good linear relationship within the dynamic range of 0.01-10 ng/mL at a limit of detection of 5.4 pg/mL HER2. In addition, good reproducibility, high specificity and acceptable accuracy were acquired for the measurement of human serum samples. Importantly, this method can be extended for quantitative monitoring other disease-related proteins by changing the corresponding antibodies.

Cation Exchange Reaction-Mediated Photothermal and Polarity-Switchable Photoelectrochemical Dual-Readout Biosensor.

Cation exchange (CE) is a burgeoning method for controlled crystal synthesis; however, its applications in bioanalysis are still in their infancy. Herein, we explored the transformation of ZnIn2S4 in properties after the CE reaction with Cu2+ ions; furthermore, the discrepancy was employed to design a dual-readout detection system of photothermal and polarity-switchable photoelectrochemical (PEC) immunoassays to realize reliable detection of carcinoembryonic antigen (CEA). In the presence of CEA, the CuO nanoparticles (CuO NPs) employed as dual-signal response probes would bond to the microplates and be acidolyzed by HCl to release Cu2+, which could replace Zn2+ and In3+ via the CE reaction. After the CE reaction is completed, the photocurrent would switch from a weak anodic photocurrent to a cathode one by using a 635 nm laser as a signal amplifier, while the photothermal signal would be enhanced with 808 nm laser illumination. On the basis of the polarity-switchable PEC strategy, CEA could be accurately detected from 0.1 to 50 ng mL-1 with a limit of detection (LOD) of 48 pg mL-1 (S/N = 3). Moreover, the photothermal assay for CEA detection possesses a linear range from 0.5 to 100 ng mL-1 with a LOD of 0.21 ng mL-1. In addition, the designed sensing platform only relies on devices with portability that are permitted for point-of-care detection.

Smartphone-based photoelectrochemical immunoassay for carcinoembryonic antigen based on BiOCl/CuBi2O4 heterojunction.

Photoelectrochemical (PEC) immunoassay has been widely developed for biomarker detection, but most include heavy and expensive instruments that are not suited for portable and on-site detection. In this work, the PEC immunoassay platform for mobile phones was reported for flexible, rapid, low-cost detection of carcinoembryonic antigen (CEA). The PEC detection platform was successfully composed of disposable screen-printed carbon electrodes, a micro-electrochemical workstation, a flashlight (the excitation light source), and a smartphone with a companion software with a micro-electrochemical workstation for rapid and on-site detection of target biomarkers. In this portable smartphone-based PEC system, the S-scheme heterojunction BiOCl/CuBi2O4 was effectively excited due to the efficient electron transfer rate and excellent photocurrent response under visible light. Specifically, the sandwich-type immunoreaction for capturing target biomarkers introduced alkaline phosphatase (ALP) labeled gold nanoparticles (Au NPs). The addition of CEA increased the ascorbic acid (AA) content and enhanced the photocurrent. The proposed immunoassay presented a good linear with the logarithm of CEA concentrations range within 0.01-40 ng mL-1, and the detection limit of 3.5 pg mL-1 (S/N = 3). Therefore, the portable detection platform offered an implementable approach to the development of miniaturized and portable photoelectrochemical detectors and on-site detection technology.

Block-Polymer-Restricted Sub-nanometer Pt Nanoclusters Nanozyme-Enhanced Immunoassay for Monitoring of Cardiac Troponin I.

Noble-metal nanozymes have demonstrated great potential in various fields. However, aggregation of single-particle nanoparticles severely affects their exposed catalytically active sites to the extent of exhibiting weak enzyme-like activity. Here, we present an organic block surfactant (polyvinylpyrrolidone, PVP) to construct monodisperse water-stable Pt nanoclusters (Pt NCs) for an enhanced immunoassay of cardiac troponin I (cTnI). The PVP-modified Pt NC nanozyme exhibited up to 16.3 U mg-1 peroxidase-mimicking activity, which was mainly attributed to the ligand modification on the surface and the electron-absorbing effect of the ligand on the Pt NCs. The PVP-modified Pt NCs have a lower OH-transition potential, as determined by density functional theory. Under optimized experimental conditions, the enhanced nanozyme immunoassay strategy exhibited an ultrawide dynamic response range of 0.005-50 ng mL-1 for cTnI targets with a detection limit of 1.3 pg mL-1, far superior to some reported test protocols. This work provides a designable pathway for the design of artificial enzymes with high enzyme-like activity to further expand the practical range of enzyme alternatives.

Multiorbital DNA walker nanoprobe for portable photothermal detection based on H2S etching of cubic Prussian blue.

In the developed assay, multiorbital 3D DNA walker (MO DNA walker) was applied as signal amplified protocol for enhancing the detection signal of the photothermal biosensor, which was designed for sensitive detection of miRNA based on the H2S triggered conversation of photothermal reagent. When the target molecule is present, the DNA walking strand was released and then hybridize with track strands. The landing of walking particles (WPT) on the tracking particles (TPT) promotes the relative movement of the WPT around TPT, thus releasing large amount of horseradish peroxidase (HRP) with the aid of DNAzyme. After reacting with Na2S2O3 and H2O2, multiple H2S can be generated in situ based on the catalytic ability of HRP. Meanwhile, cubic Prussian blue (CPB) was synthesized and exhibited superior photothermal response, which can be served as efficient photothermal reagent and H2S responsive acceptor. Significantly, the photothermal signal of CPB could be obviously reduced after challenged with H2S ascribed to synchronous reaction between the ferric ion (Fe3+) and H2S. The improved walking area and freedom enable significant signal amplification, enhancing the biosensor's performance. Under ideal circumstances, the proposed photothermal assay demonstrated excellent performance for determination of miRNA-21.

FeNC nanozyme-based electrochemical immunoassay for sensitive detection of human epidermal growth factor receptor 2.

The proof-of-concept of sensitive electrochemical immunoassay for the quantitative monitoring of human epidermal growth factor receptor 2 (HER2) is reported. The assay is carried out on iron nitrogen-doped carbon (FeNC) nanozyme-modified screen-printed carbon electrode using chronoamperometry. Introduction of target HER2 can induce the sandwiched immunoreaction between anti-HER2 monoclonal antibody-coated microplate and biotinylated anti-HER2 polyclonal antibody. Thereafter, streptavidin-glucose oxidase (GOx) conjugate is bonded to the detection antibody. Upon addition of glucose, 3,3',5,5'-tetramethylbenzidine (TMB) is oxidized through the produced H2O2 with the assistance of GOx and FeNC nanozyme. The oxidized TMB is determined via chronoamperometry. Experimental results revealed that electrochemical immunosensing system exhibited good amperometric response, and allowed the detection of target HER2 as low as 4.5 pg/mL. High specificity and long-term stability are acquired with FeNC nanozyme-based sensing strategy. Importantly, our system provides a new opportunity for protein diagnostics.