Antigen-Down PEC Immunosensor for CYFRA21-1 Detection Based on Photocurrent Polarity Switching Strategy

Biotin-functionalized nanoparticles: an overview of recent trends in cancer detection

Electrochemical bio-sensing is a potent and efficient method for converting various biological recognition events into voltage, current, and impedance electrical signals. Biochemical sensors are now a common part of medical applications, such as detecting blood glucose levels, detecting food pathogens, and detecting specific cancers. As an exciting feature, bio-affinity couples, such as proteins with aptamers, ligands, paired nucleotides, and antibodies with antigens, are commonly used as bio-sensitive elements in electrochemical biosensors. Biotin-avidin interactions have been utilized for various purposes in recent years, such as targeting drugs, diagnosing clinically, labeling immunologically, biotechnology, biomedical engineering, and separating or purifying biomolecular compounds. The interaction between biotin and avidin is widely regarded as one of the most robust and reliable noncovalent interactions due to its high bi-affinity and ability to remain selective and accurate under various reaction conditions and bio-molecular attachments. More recently, there have been numerous attempts to develop electrochemical sensors to sense circulating cancer cells and the measurement of intracellular levels of protein thiols, formaldehyde, vitamin-targeted polymers, huwentoxin-I, anti-human antibodies, and a variety of tumor markers (including alpha-fetoprotein, epidermal growth factor receptor, prostate-specific Ag, carcinoembryonic Ag, cancer antigen 125, cancer antigen 15-3, etc.). Still, the non-specific binding of biotin to endogenous biotin-binding proteins present in biological samples can result in false-positive signals and hinder the accurate detection of cancer biomarkers. This review summarizes various categories of biotin-functional nanoparticles designed to detect such biomarkers and highlights some challenges in using them as diagnostic tools.

A magnetic plasma Fe3O4@Cu@Cu2O photoelectrochemical sensor for the detection of fumonisin B1

Fumonisin B1 (FB1) is a mycotoxin, a water-soluble metabolite produced by Fusarium cepacia, which mainly contaminates grain and its products and is acutely toxic and potentially carcinogenic to certain domestic animals. In this work, plasma nanocomposites of Fe3O4@Cu@Cu2O with magnetic and optoelectronic properties were synthesized as a sensing platform. On one hand, the surface plasmon resonance (SPR) of metallic Cu accelerates the electron transfer rate. On the other hand, plasma-induced resonance energy transfer of metals and semiconductors can improve the utilization efficiency of light energy. A split photoelectrochemical (PEC) sensor based on Fe3O4@Cu@Cu2O was proposed for the detection of FB1. The sensor has a wide linear range of 1.0-10 000 pg mL-1 and a low detection limit of 0.28 pg mL-1 (LOD, S/N = 3), which can realize the specific detection of FB1 in real samples.

Applications of Biosensors in Bladder Cancer

Bladder cancer (BC) is the tenth most common cancer globally, predominantly affecting men. Early detection and treatment are crucial due to high recurrence rates and poor prognosis for advanced stages. Traditional diagnostic methods like cystoscopy and imaging have limitations, leading to the exploration of noninvasive methods such as liquid biopsy. This review highlights the application of biosensors in BC, including electrochemical and optical sensors for detecting tumor markers like proteins, nucleic acids, and other biomolecules, noting their clinical relevance. Emerging therapeutic approaches, such as antibody-drug conjugates, targeted therapy, immunotherapy, and gene therapy, are also explored, the role of biosensors in detecting corresponding biomarkers to guide these treatments is examined. Finally, the review addresses the current challenges and future directions for biosensor applications in BC, highlighting the need for large-scale clinical trials and the integration of advanced technologies like deep learning to enhance diagnostic accuracy and treatment efficacy.

Dual-mode biosensor using Tb-Cu MOF@Au nanoenzyme to effectively quench the photocurrent of Bi2O3/Bi2S3/AgBiS2 heterojunction and emit fluorescence for neuron-specific enolases detection

A novel dual-mode biosensor was constructed for the ultrasensitive detection of neuron-specific enolase (NSE), utilizing Tb-Cu MOF@Au nanozyme as the signal label to effectively quench the photoelectrochemical (PEC) signals of Bi2O3/Bi2S3/AgBiS2 composites and initiate fluorescent (FL) signals. First, Bi2O3/Bi2S3/AgBiS2 heterojunction with excellent photoelectric activity was selected as the substrate material to provide a stable photocurrent. The well-matched energy levels significantly enhanced the separation and transfer of photogenerated carriers. Second, a strategy of consuming ascorbic acid (AA) by Tb-Cu MOF@Au nanozyme was introduced to improve the sensitivity of the PEC/FL biosensor. Tb-Cu MOF@Au not only could catalyze the oxidation of AA, but the steric effect further reduced the contact of AA with the substrate. More importantly, in the presence of H2O2, a significant fluorescence was produced from Tb3+ sensitized by the oxidation products of AA. Based on the above strategies, a highly stable and sensitive dual-mode biosensor was proposed for accurate NSE determination. Third, the developed dual-mode biosensor demonstrated excellent performance in detecting NSE. In this study, the PEC method demonstrated a wide detection range from 0.00005 to 200 ng/mL with a low detection limit of 20 fg/mL. The FL method exhibited a linear range from 0.001 to 200 ng/mL with a detection limit of 0.65 pg/mL. The designed biosensor showed potential practical implications in the accurate detection of disease markers.

Sulfur defect-engineered Bi2S3-x/In2S3-y mediated signal enhancement of photoelectrochemical sensor for lead ions detection

Lead ions (Pb2+) are heavy metal ions that are harmful to living organisms and ecosystems. It is important to realize sensitive detection of Pb2+ in the environment. In this study, a signal enhancement photoelectrochemical (PEC) sensor with high sensitivity was constructed for the detection of Pb2+. Firstly, to obtain excellent electron transfer performance, sulfur defect-engineered Bi2S3-x/In2S3-y mediated signal enhancement formed by Bi2S3 and In2S3 with well-matched structure in terms of energy level as the substrate materials. In this case, the introduction of sulfur vacancies further affects the electronic structure of the material, which significantly improves the electrical conductivity and effectively increases the electron transfer rate. In addition, the as-synthesized Cu@Cu2O nanosphere is chosen as the marker to accelerate the electron transfer through the surface plasmon resonance effect of Cu. The constructed sensor was able to detect Pb2+ in the range of 1 ng mL-1-100 μg mL-1 with a limit of detection of 19.2 pg mL-1. The sensor exhibits good reproducibility, specificity, and stability, indicating such PEC sensor can achieve the sensitive detection of Pb2+ in the environment. This work paves a new way for the construction of PEC sensors and the specific PEC detection of Pb2+ in environmental waters.

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.

Oxygen vacancies-driven signal enhanced photoelectrochemical sensor for mercury ions detection

Mercury ion (Hg2+) poses a serious threat to human health due to its high toxicity. In this study, a smartphone-based photoelectrochemical sensor based on oxygen vacancies (OVs) driven signal enhancement for mercury ion detection was designed. BiVO4-x/Bi2S3/AuNPs were combined with T-Hg2+-T recognition mode to construct a multi-sandwich photoelectrochemical sensor. On the one hand, the OVs can increase the adsorption of light by the materials and enhance the photocurrent response as well as the superconductivity of Au NPs to accelerate the charge transfer at the electrode interface. On the other hand, the multi-sandwich structure was exploited to increase the binding site of Hg2+, as well as the T-Hg2+-T structure for sensitive recognition of Hg2+ and signal amplification. The sensor showed good linearity for Hg2+ concentration in the range of 0.1 nM-1.0 μM with a detection limit of 4.8 pM (S/N = 3). Eventually the smartphone-based real-time detection sensor is expected to contribute to the future analysis of heavy metal ions.

Metal-organic-framework-confined quantum dots enhance photocurrent signals: A molecularly imprinted photoelectrochemical cathodic sensor for rapid and sensitive tetracycline detection

BACKGROUND

Tetracycline (TC), a cost-effective broad-spectrum antibacterial drug, has been excessively utilized in the livestock and poultry industry, leading to a serious overabundance of TC in livestock wastewater. However, conventional analytical methods such as liquid chromatography and gas chromatography face challenges in achieving sensitive detection of trace amounts of TC in complex substrates. Therefore, it is imperative to develop a highly sensitive and anti-interference analytical method for the detection of tetracycline in livestock wastewater.

RESULTS

A porphyrin-based MOF (PCN-224)-confined carbon dots (CDs) material (CDs@PCN-224) was synthesized by a "bottle-around-ship" strategy. The reduced carrier migration distance is conducive to the separation of electron-hole pairs and enhanced the photocurrent signal due to the tight coupling of CDs and PCN-224. Further, molecularly imprinted polymer (MIP) was synthesized by rapid in-situ UV-polymerization and employed as a recognition element. The specific recognition of the target by imprinted cavities blocks electron transfer, resulting in a "turn off" response signal, thus realizing the selective detection of TC. Under optimal conditions, the constructed MIP-PEC cathodic sensor detected 1.00 × 10-12 M to 1.00 × 10-7 M of TC sensitively, with a limit of detection of 3.72 × 10-13 M. In addition, the proposed MIP-PEC sensor demonstrated good TC detection performance in actual livestock wastewater.

SIGNIFICANCE

The strategy based on MOF pore-confined quantum dots can effectively enhance the photocurrent response of the photosensitive substrate. Simultaneously, the MIP constructed by in-situ rapid UV-polymerization showed excellent anti-interference and reusable properties. This work provides a promising MIP-PEC cathodic sensing method for the rapid and sensitive detection of antibiotics in complex-matrix environmental samples.

Efficient sensitization of CdTe QDs towards PTCDA for sensitive photoelectrochemical Hg2+ assay

Herein, a sensitive photoelectrochemical (PEC) biosensor was designed for the detection of mercury ions (Hg2+) on the basis of the efficient sensitization of cadmium telluride quantum dots (CdTe QDs) towards 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and the significant quenching ability of a thymine-Hg2+-thymine (T-Hg2+-T) structure. The proposed CdTe QD/PTCDA sensitized structure was successfully constructed via continuous incubation of PTCDA and CdTe QDs on the glassy carbon electrode (GCE) interface, which embraced strong light absorption capacity and high carrier separation efficiency, giving rise to a remarkably improved initial photocurrent response. Notably, the PEC signal generated from the CdTe QD/PTCDA sensitized structure was almost fivefold higher than that of PTCDA owing to the efficient sensitization of CdTe QDs towards PTCDA. Once target Hg2+ ions were added, a T-rich S1 strand modified on the surface of 1-hexanethiol (HT)/S1/gold nanoparticles (Au NPs)/CdTe QDs/PTCDA/GCE immediately reacted with Hg2+ to produce multiple stable T-Hg2+-T structures. Therefore, the initial PEC signal would be considerably quenched by a high steric hindrance effect derived from the T-Hg2+-T structures. As a result, a quenched PEC response could achieve the detection of Hg2+ in concentrations ranging from 100 fM to 1000 nM. More importantly, the combination of the CdTe QDs/PTCDA sensitization structure and the T-Hg2+-T structure paves a promising pathway to developing a novel PEC biosensing platform for Hg2+ detection and also provides a favorable strategy for monitoring environmental pollution related to Hg2+.

Dual-mode self-powered photoelectrochemical and colorimetric determination of procalcitonin accomplished by multienzyme-expressed Ni4Cu2 bimetallic hollow nanospheres and spherical nanoflower-MoS2/Cu2ZnSnS4/Bi2S3

Bacterial infections, viral infections and autoimmune diseases pose a considerable threat to human health. Procalcitonin (PCT) has emerged as a biomarker for the detection of these diseases. To ensure accurate and reliable results, we propose a dual-mode approach that incorporates self-validation and self-correction mechanisms. Herein, we develop a dual-mode self-powered photoelectrochemical (PEC) and colorimetric sensor to determine PCT. The self-powered PEC sensor was constructed with a photoanode of spherical nanoflower-MoS2/Cu2ZnSnS4/Bi2S3 material and a photocathode of CuInS2 material. Ni4Cu2 bimetallic hollow nanospheres (BHNs) possess superoxide dismutase and catalase performance, which facilitate superoxide anion radical (·O2-) and H2O2 circulating generation, promoting the separation of photogenerated electrons and holes to amplify photocurrent signal. Thus Ni4Cu2 BHNs is used as a marker material for PEC sensor. Meanwhile, in colorimetric mode, Ni4Cu2 BHNs converts blue oxTMB to a colourless TMB for colorimetric detection of PCT. Based on this principle, dual-mode determination of PCT with high sensitivity is achieved. The dual-mode method not only demonstrates outstanding properties and practicability, but also presents an effective, highly efficient and reliable method for detecting PCT.

Triple signal-enhanced electrochemiluminescence strategy using iron-based metal-organic frameworks modified with Ru(II) complexes for carcino-embryonic antigen detection

The development of a highly efficient electrochemiluminescence (ECL) emitter represents an effective strategy for enhancing the sensitivity and repeatability of ECL immunosensors. In this study, a sandwich-type ECL immunosensor with triple enhancement was developed to detect carcino-embryonic antigen (CEA). This sensor is based on a porous structure of iron-based metal-organic framework (NH2-MIL-88(Fe)), encapsulating the luminescent tris(2,2'-bipyridine)ruthenium (II) (Ru (bpy)32+), Au@MoS2 with a 3D nanoflower structure as an enhanced substrate. In this system, the MOFs framework encapsulated luminophore was realized to solve its water solubility to reach stable luminescence, as well as the triple enhancement effect based on the principle of amino catalysis, Mo4+/Mo6+ active site conversion, and gold nanoparticles (Au NPs) promotion, which significantly enhanced the detection sensitivity. Furthermore, the ECL immunosensor demonstrated successful application in the highly sensitive and selective detection of CEA, achieving a detection limit of 38.9 fg mL-1. The sensor demonstrates remarkable sensitivity, specificity, stability, repeatability, and practicality in the analysis of human serum samples. This investigation presents a highly effective approach for the ultrasensitive detection of trace proteins.

A paper-based photoelectrochemical aptsensor using near-infrared light-responsive AgBiS2 nanoflowers as probes for the detection of Staphylococcus aureus in pork

Staphylococcus aureus is a gram-positive bacterium that can easily cause outbreaks of food-borne diseases. In this work, a signal-enhanced three-dimensional paper-based photoelectrochemical (PEC) aptsensor for the rapid and sensitive determination of S. aureus was developed. Specifically, gold nanoparticles (AuNPs) were electrodeposited on a paper-based working electrode to provide binding sites for a sulfhydryl-functionalized aptamer. Subsequently, S. aureus was captured with high specificity by a carboxyl-functionalized aptamer modified with amino-functionalized AgBiS2 nanoflowers (NH2-AgBiS2 NFs), which functionalized as PEC probes that generated strong photocurrent under irradiation with 980-nm light. By exploiting the "aptamer-target-aptamer" PEC sensing platform, the rapid and ultrasensitive detection of S. aureus was achieved. The sensor had a wide linear range of 20 to 2 × 107 CFU/mL and low limit of detection of 4 CFU/mL. Further, the applicability of the as-prepared aptsensor was successfully certified for the analysis of pork samples artificially contaminated with S. aureus.

Application of DNA-fueled molecular machines in food safety testing

Food is consumed by humans, which is indispensable to human life. Therefore, considerable attention of the whole society has been paid to food safety. Over the last few years, dramatic social development has brought new challenges to food safety, making developing new and quick methods for on-site food safety testing an important necessity. As a result, DNA-fueled molecular machines, characterized by high efficiency, accuracy, and sensitivity in testing, have come into the spotlight, based on which sensors can be constructed to detect toxic and harmful substances in food products. This study reviewed recent research on several DNA-fueled molecular machines, including DNA tweezers, DNA walkers, and DNA origami, for rapidly detecting toxic and harmful substances. Based on the above studies, the sensitivity and timeliness of several DNA molecular machines were summarized and compared, and the development prospect of DNA fuel molecular machines in the field of food safety detection was prospected.

Photocurrent Polarity Switchable Sensing of Hyaluronidase Activity by Regulating Electrostatic Interactions between Two Semiconductors

Photocurrent polarity switchable photoelectrochemical (PEC) sensing has superior accuracy and anti-interference ability to conventional PEC sensing. The development of a novel strategy for photocurrent polarity switchable sensing is of great interest. Herein, a novel strategy for photocurrent polarity switchable sensing is reported by regulating electrostatic interactions between two semiconductor photoactive materials. Hyaluronic acid (HA)-modified CuO nanosheets show a negatively charged surface, which prevents the attachment of CuO nanosheets to negatively charged CdS nanodendrite-modified photoelectrodes because of the strong electrostatic repulsion. In the presence of hyaluronidase (HAase), the specific hydrolysis of HA on the surface of CuO by HAase can yield a positively charged surface, so CuO can be attached to a CdS-modified photoelectrode via electrostatic attraction, leading to photocurrent polarity switching. The photocurrent polarity switchable detection of HAase activity is achieved with an ultralow detection limit of 2 × 10-3 U mL-1 and a wide linear detection range between 0.01 and 100 U mL-1. This work provides a new and effective photocurrent polarity switching strategy for PEC sensing and a simple and efficient method for detecting HAase activity.

G-Quadruplex/Hemin-Mediated Polarity-Switchable and Photocurrent-Amplified System for Escherichia coli O157:H7 Detection

The contamination of food by pathogens is a serious problem in global food safety, and current methods of detection are costly, time-consuming, and cumbersome. Therefore, it is necessary to develop rapid, portable, and sensitive assays for foodborne pathogens. In addition, assays for foodborne pathogens must be resistant to interference resulting from the complex food matrix to prevent false positives and negatives. In this study, hemin and reduced graphene oxide-MoS2 sheets (GMS) were used to design a near-infrared (NIR)-responsive photoelectrochemical (PEC) aptasensor with target-induced photocurrent polarity switching based on a hairpin aptamer (Hp) with a G-quadruplex motif. A ready-to-use analytical device was developed by immobilizing GMS on the surface of a commercial screen-printed electrode, followed by the attachment of the aptamer. In the presence of Escherichia coli O157:H7, the binding sites of Hp with the G-quadruplex motif were opened and exposed to hemin, leading to the formation of a G-quadruplex/hemin DNAzyme. Crucially, after binding to hemin, the charge transfer pathway of GMS changes, resulting in a switch of the photocurrent polarity. Further, G-quadruplex/hemin DNAzyme enhanced the cathodic photocurrent, and the proposed sensor exhibited a wide linear range ((25.0-1.0) × 107 CFU/mL), a low limit of detection (2.0 CFU/mL), and good anti-interference performance. These findings expand the applications of NIR-responsive PEC materials and provide versatile PEC methods for detecting biological analytes, especially for food safety testing.

Photocurrent Polarity Reversal Induced by Electron-Donor Release for the Highly Sensitive Photoelectrochemical Detection of Vascular Endothelial Growth Factor 165

Photocurrent polarity reversal is a switching process between the anodic and cathodic pathways and is critical for eliminating false positivity and improving detection sensitivity in photoelectrochemical (PEC) sensing. In this study, we construct a PEC sensor with excellent photocurrent polarity reversal induced by ascorbic acid (AA) as an electron donor with the energy level matching the photoactive material zirconium metal-organic framework (ZrMOF). The ZrMOF-modified electrode demonstrates cathodic photocurrent in the presence of O2 as an electron acceptor, while the anodic photocurrent is generated in the presence of AA, achieving photocurrent polarity reversal. By the in situ release of AA from AA-encapsulated apoferritin modified with DNA 2 (AA@APO-S2) as a detection tag in the presence of trypsin after the recognition of hairpin DNA-modified indium tin oxide to the reaction product of aptamer/DNA 1 with the target protein and the following rolling cycle amplification for introducing the detection tag to the sensing interface, the reversed photocurrent shows an enhanced photocurrent response to the target protein, leading to a highly sensitive PEC sensing strategy. This strategy realizes the detection of vascular endothelial growth factor 165 with good specificity, a wide linear range, and a low detection limit down to 5.3 fM. The actual sample analysis offers the detection results of the proposed PEC sensor comparable to those of commercial enzyme-linked immunosorbent assay tests, indicating the promising application of the photocurrent polarity reversal-based PEC sensing strategy in biomolecule detection and clinical diagnosis.

Polarity Conversion of the Ag2S/AgInS2 Heterojunction by Radical-Induced Positive Feedback Polydopamine Adhesion for Signal-Switchable Photoelectrochemical Biosensing

Efficient tuning of the polarity of photoactive nanomaterials is of great importance in improving the performance of photoelectrochemical (PEC) sensing platforms. Herein, polarity of the Ag2S/AgInS2 heterojunction is converted by radical-induced positive feedback polydopamine (PDA) adhesion, which is further employed to develop a signal-switchable PEC biosensor. In the nanocomposites, Ag2S and AgInS2 achieve electron-hole separation, exhibiting a strong anodic PEC response. Under the irradiation of light, the Ag2S/AgInS2 heterojunction is able to produce superoxide radical and hydroxyl radical intermediate species, leading to the polymerization of dopamine (DA) and the subsequent adhesion of PDA onto the Ag2S/AgInS2 heterojunction (Ag2S/AgInS2@PDA). By constructing a new electron-transfer pathway with PDA, the polarity of the Ag2S/AgInS2 heterojunction is converted, and the PEC response changes from anodic to cathodic photocurrents. In addition, since the photoreduction activity of PDA is stronger than that of the Ag2S/AgInS2 heterojunction, more superoxide radical can be produced by Ag2S/AgInS2@PDA once PDA is generated, thereby promoting the generation of PDA. Consequently, a positive feedback mechanism is established to enhance the polarity conversion of the Ag2S/AgInS2 heterojunction and amplify the responding to DA. As a result, the bioanalytical method is capable of sensitively quantifying DA in 10 orders of magnitude with an ultralow limit of detection. Moreover, the applicability of this biosensor in real samples is identified by measuring DA in fetal bovine serum and compared with a commercial ELISA method. Overall, this work offers an alternative perspective for adjusting photogenerated carriers of nanomaterials and designing high-performance PEC biosensors.

Competitive photoelectrochemical aptamer sensor based on a Z-scheme Fe2O3/g-C3N4 heterojunction for sensitive detection of lead ions

Lead ion (Pb2+) is one of the heavy metal contaminants within the environment, which can seriously affect biological health. Thus, it is very important to detect lead ions, especially exceeding the standard concentration (100 ng/mL). In this work, we have developed a photoelectrochemical (PEC) aptamer sensor with Z-scheme Fe2O3/g-C3N4 heterojunction as a substrate material for sensitive detection of Pb2+. Specifically, Fe2O3/g-C3N4 is employed as a substrate with a powerful and stable photocurrent response. Au and DNA-1 connected to the substrate material via the Au-S bond and increased the electron conduction. Marking DNA-2 with ZnO effectively reduced the light absorption intensity resulting in a lower photocurrent response. Surprisingly, the Pb2+ PEC sensor showed good linearity in the detection range of 62 pg/mL to 1 μg/mL with a detection limit as low as 7.9 pg/mL (S/N = 3). The sensor showed stable recovery and low relative standard deviation in real sample detection. Additionally, the sensor exhibited excellent stability, selectivity, and reproducibility. The reproducibility of the electrodes was evaluated, and the accuracy of the individual electrode current values was calculated to range from 0.5% to 2.71% with an RSD of 1.74%. Such PEC sensor guarantees to supply a brand-new approach to the detection of Pb2+.

PEC-SERS Dual-Mode Detection of Foodborne Pathogens Based on Binding-Induced DNA Walker and C3N4/MXene-Au NPs Accelerator

In this paper, a photoelectrochemical (PEC)-surface-enhanced Raman scattering (SERS) dual-mode biosensor is constructed coupled with a dual-recognition binding-induced DNA walker with a carbon nitride nanosheet (C3N4)/MXene-gold nanoparticles (C/M-Au NPs) accelerator, which is reliable and capable for sensitive and accurate detection of Staphylococcus aureus (S. aureus). Initially, a photoactive heterostructure is formed by combining C3N4 and MXene via a simple electrostatic self-assembly as they possess well-matched band-edge energy levels. Subsequently, in situ growth of gold nanoparticles on the formed surface results in better PEC performance and SERS activity, because of the synergistic effects of surface plasmon resonance and Schottky barrier. Furthermore, a three-dimensional, bipedal, and dual-recognition binding-induced DNA walker is introduced with the formation of Pb2+-dependent DNAzyme. In the presence of S. aureus, a significant quantity of intermediate DNA (I-DNA) is generated, which can open the hairpin structure of Methylene Blue-tagged hairpin DNA (H-MB) on the electrode surface, thereby enabling the switch of signals for the quantitative determination of S. aureus. The constructed PEC-SERS dual-mode biosensor that can be mutually verified under one reaction effectively addresses the problem of the low detection accuracy of traditional sensors. Experimental results revealed that the effective combination of PEC and SERS is achieved for amplification detection of S. aureus with a detection range of 5-108 CFU/mL (PEC) and 10-108 CFU/mL (SERS), and a detection of limit of 0.70 CFU/mL (PEC) and 1.35 CFU/mL (SERS), respectively. Therefore, this study offers a novel and effective dual-mode sensing strategy, which has important implications for bioanalysis and health monitoring.

Facile preparation of poly-(styrene-co-maleic anhydride) encapsulated Iridium(III) complexes as highly efficient electrochemiluminescence indicators for sensitive immunoassay of CYFRA 21-1

Exploring facile strategy for developing highly efficient emitters using water-insoluble luminophores has become a vital topic in electrochemiluminescence (ECL) immunoassay. In this work, an ECL-active and water-dispersive iridium(III) complex-based polymer dots (IrPdots) was fabricated by encapsulating water-insoluble tris[1-phenylisoquinolinato-C2, N] iridium(III) complexes [Ir(piq)₃] into poly-(styrene-co-maleic anhydride) (PSMA) matrix by a controllable nanoprecipitation process. The obtained IrPdots generated strong ECL signals in the presence of tri-n-propylamine (TPrA) and were used to label detection antibody (Ab₂) to act as ECL probes to indicate the signal changes when analyzing target antigen. To construct a sandwich immunosensor, Pd nanoparticles (NPs) decorated MoS₂/Ti₃C₂T_x MXene nanocomposites (MoS₂/Ti₃C₂T_x MXene/Pd) were fabricated as substrates to bind capture antibody (Ab₁), which could further amplify ECL signals via a coreaction-accelerating pathway to improve the detection sensitivity. When the cytokeratin 19 fragment 21-1 (CYFRA 21-1) was chosen as model analyte, the developed immunosensor displayed a good linear relationship ranging from 0.1 pg/mL to 50 ng/mL with a low detection limit of 95 fg/mL (S/N = 3) was achieved as well. This research proposed a facile and effective method of fabricating IrPdots as ECL probes for immunoassay using water-insoluble iridium complexes, which expanded the application scope of those water-insoluble luminophores for aqueous bioanalysis.

Ultrasensitive Photocathodic Biosensor Based on the Cu2O/PTB7-Th/PDA+ Composite with Enhanced Photoelectrochemical Performance for the Detection of MicroRNA-375-3p

Herein, an ultrasensitive photocathodic biosensor was fabricated based on Cu2O/PTB7-Th/PDA+ photoactive materials with high photocarrier separation efficiency for the detection of microRNA-375-3p. Impressively, the photocathodic signal of the Cu2O material was significantly enhanced by using PTB7-Th as an energy level-matching photoactive material to enhance the bulk charge separation and N,N-bis (2-(trimethylammoniumiodide) propylene) perylene-3,4,9,10-tetracarboxydiimide (PDA+) as an interfacial charge transfer mediator to efficiently suppress charge recombination at the photoelectrode/electrolyte interface. Compared with the pristine Cu2O as a photocathode, the obtained Cu2O/PTB7-Th/PDA+ exhibited a 17 times higher photocathodic signal. As a proof of concept, a PEC biosensor was fabricated by using Cu2O/PTB7-Th/PDA+ as a photoactive material and a target-triggered 3D DNA walker integrated with the dumbbell hybridization chain reaction (DHCR) as a signal amplifier to achieve the sensitive detection of microRNA-375-3p with a detection limit of 0.3 fM. This work provided a method to increase the photocurrent signal and the sensitivity of PEC-sensing platforms for the detection of biomarkers and disease diagnosis.

Dual-signal ratiometric electrochemical immunosensor constructed with snowflake-like FeSe2-AuNPs and PAA-ZIF@TB for sensitive detection of CYFRA21-1

In this study, a ratiometric electrochemical immunosensor has been developed to detect the cytokeratin 19 fragment 21-1 (CYFRA21-1) biomarker in a highly sensitive manner through a dual-signal output model. As one of signal indicators, snowflake-like FeSe₂ loaded with AuNPs (FeSe₂-AuNPs) as sensing substrate with good conductivity and large active sites provides a differential pulse voltammetry (DPV) signal at +0.4 V. Another signal indicator, toluidine blue (TB) with the water-solubility property is an excellent redox probe that can generate DPV signal at -0.3 V. To solve the water-solubility problem, the TB is absorbed with polyacrylic acid (PAA) functionalized ZIF-67 (PAA-ZIF-67), which retains the properties of ZIF-67 that are large specific surface area and strong adsorption properties. The ratio of signals, stemmed from PAA-ZIF@TB and FeSe₂-AuNPs (I_PAA-ZIF@TB/I_FeSe2-AuNPs), increases with the CYFRA21-1 concentration. Under optimal experimental conditions, CYFRA21-1 was detected in a wide dynamic range from 0.1 pg/mL to 100 ng/mL, with a lower limit of detection of 0.02 pg/mL. Looking ahead, this ratio based strategy provides prospective clinical applications for detecting other biomarkers.

Ultrasensitive Photoelectrochemical Immunoassay Strategy Based on Bi2S3/Ag2S for the Detection of the Inflammation Marker Procalcitonin

As an inflammatory marker, procalcitonin (PCT) is more representative than other traditional inflammatory markers. In this work, a highly efficient photoelectrochemical (PEC) immunosensor was constructed based on the photoactive material Bi₂S₃/Ag₂S to realize the sensitive detection of PCT. Bi₂S₃ was prepared by a hydrothermal method, and Ag₂S quantum dots were deposited on the ITO/Bi₂S₃ surface via in situ reduction. Bi₂S₃ is a kind of admirable photoelectric semiconductor nanomaterial on account of its moderate bandgap width and low binding rate of photogenerated electron holes, which can effectively convert light energy into electrical energy. Therefore, based on the energy level matching principle of Bi₂S₃ and Ag₂S, a labeled Bi₂S₃/Ag₂S PEC immunosensor was constructed, and the sensitive detection of PCT was successfully established. The linear detection range of the PEC immunosensor was 0.50 pg∙mL^-1 to 50 ng∙mL^-1, and the minimum detection limit was 0.18 pg∙mL^-1. Compared with the traditional PEC strategy, the proposed PEC immunosensor is simple, convenient, and has good anti-interference, sensitivity, and specificity, which could provide a meaningful theoretical basis and reference value for the clinical detection of PCT.

Photoelectrochemical Immunosensor Based on a 1D Fe2O3/3D Cd-ZnIn2.2Sy Heterostructure as a Sensing Platform for Ultrasensitive Detection of Neuron-Specific Enolase

Lung cancer is a high-mortality cancer related to the concentration of neuron-specific enolase (NSE). In this work, a sandwich-type photoelectrochemical (PEC) immunosensor was constructed for ultrasensitive detection of NSE, which is based on iron trioxide/indium zinc cadmium sulfide (Fe₂O₃/Cd-ZnIn_2.2S_y) as a sensing platform and Ag-modified polyaniline (Ag@PANI) as a signal amplification label. The 1D Fe₂O₃ porous nanorods with a large specific surface area were synthesized by calcination of Fe-MIL-88A and etching of NaOH. To improve the photocurrent response, the 3D architecture Cd-ZnIn_2.2S_y was combined with the 1D Fe₂O₃ porous nanorods to form a 1D Fe₂O₃/3D Cd-ZnIn_2.2S_y heterostructure. Specifically, the Fe₂O₃/Cd-ZnIn_2.2S_y heterostructure with a good energy level matching (the two can form a stepped energy level matching, which accelerates the transfer rate of electrons) can improve the separation efficiency of electron-hole pairs (e^-/h⁺) under visible light irradiation, which enhances the photocurrent response. Ag@PANI has a strong electron transport capability and can be used as a secondary antibody marker for the signal amplification of the immunosensor. The sensor exhibits a good linear detection range of 100 fg/mL to 100 ng/mL with a low detection limit of 33.5 fg/mL. Moreover, the constructed sandwich-type PEC immunosensor shows good performance and possesses excellent specificity, selectivity, and stability over a period of 4 weeks for NSE detection. With these excellent properties, the immunosensor can be extended to analyze and diagnose other disease biomarkers.