Silver nanoparticles (Ag·NPs) show promising advantages in electrochemiluminescence (ECL) owing to their favorable optical properties and biocompatibility. However, their susceptibility to oxidation and degradation in the presence of air adversely affects ECL intensity. In this study, we employed a sandwich sensing platform using silica-coated silver nanoparticles (Ag@SiO2) as a novel luminescent material and cerium dioxide (CeO2) as an ECL signal quencher for sensitive neuro-specific enolase (NSE) detection. The core-shell structure protected Ag NPs within the silica (SiO2) layer, enhancing their ECL luminescence properties by reducing external environmental influence and preventing Ag NPs aggregation. Amino-functionalized CeO2 efficiently diminished Ag@SiO2 ECL emission through electron transfer, resulting in a \"signal-off\" detection mode with high sensitivity and accuracy. The detection limit reached 1.66 fg/mL, and the detection range spanned from 100 fg/mL to 500 ng/mL, showcasing a powerful biomolecule detection strategy.

Antibiotic usage has become very widespread in aquaculture, and the abuse or overuse of antibiotics has led to the evolution of antibiotic-resistance bacteria, which has adverse effects on aquatic products and ecosystems. Moreover, this evolution can potentially cause harm to human health. Thus, there is an urgent need for diagnostic tools for antibiotic-resistant microorganisms. Herein, we proposed a signal-off Cas14a1-based platform (SOCP) for the detection of methicillin-resistant Staphylococcus aureus (MRSA). In this SOCP, we have designed single-stranded DNA (ssDNA) that not only can activate the trans-cleavage ability of dual Cas14a1-sgRNA complex but also can be used as the primers for the amplified methicilin-resistant gene (mecA). When MRSA is present, the primers can be transformed into products with amplification, leading to the signal decrease of trans-cleavage activity of Cas14a1. The SOCP showed high specificity and fair sensitivity for mecA gene and MRSA. In the detection of real samples, this platform also showed consistent results compared with qPCR. The SOCP could provide an alternative tool for the diagnosis of antibiotic-resistant bacteria in aquaculture, food industry and other fields.

In order to achieve rapid and sensitive detection of CYFRA 21-1, a signal-off photoelectrochemical (PEC) immunosensor was devised with NiCo2O4/CdIn2S4/In2S3 heterojunction photoactive materials as sensing platform and ReS2@Au NPs as the secondary antibody labels amplifying signal based on the energy band-matching cascade structure and double suppression effect. NiCo2O4 possessed a faster charge transfer rate due to the abundance of redox electron pairs (Co3+/Co2+ and Ni3+/Ni2+). To further improve the PEC properties of NiCo2O4 under visible light, CdIn2S4 with matching bandgap energy was selected to form heterojunction with NiCo2O4 and sensitized with In2S3. The proposed heterojunctions with well-matched band structure promoted the transfer of photo-generated carriers and were exploited as signal transducers for immobilization of antibodies and recognition of CYFRA 21-1. Furthermore, a novel urchin-like p-type ReS2 semiconductor nanostructure functionalized by Au NPs was firstly used as a nanolabel to quench the signal. On the one hand, the Schottky heterojunction generated by ReS2 and Au NPs could compete with the transducer substrate for both light and electron donors. On the other hand, the large space steric hindrance of ReS2 prevented contact between the matrix and AA. Subsequently, the sensor was sensitive in a wide range of concentrations for CYFRA 21-1 (0.0001-50 ng/mL), and the detection limit was 0.05 pg/mL.

the accurate, reliable and specific analysis of foodborne pathogenic bacteria is vital for human health and safety. Staphylococcus aureus (S. aureus), as a common bacterium, is regularly found in food, water, and other biological samples. Herein, a signal-off electrochemical DNA sensor (E-DNA sensor) was designed for the sensitive detection ofS. aureusamplified withthecombination of a dna walker and pb2+-specific dnazyme. In this work, vancomycin functionalized gold nanoclusters (Van@Au NCs) and an aptamer strand as identification units were modified at the termini of two proximity probes. upon the addition of targetS. aureus, a dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pb2+-dependent dnazyme, achieving the conversion of oneS. aureus to many intermediate dna (t) strands. then, the released t strands hybridized with methylene blue-tagged hairpin dna (h-mb) on the electrode. consequently, the conformational alteration of t strands reduced the electron transfer efficiency of mb to the electrodeinterface (signal-off). therefore, sensitive analysis of S. aureus was readily acquired within a range of 10-107 CFU/mL and a low detection limit at 1 CFU/mL. Undoubtedly, dual recognition by aptamer and vancomycin in an integrated scheme brought about a good recognition performance of S. aureus in complex samples, as well as an efficient annihilation of harmful pathogenic bacteria during the experiment.

Developing new self-powered sensors is highly demanded for smart portable electronic devices. Herein, a novel visible-light-driven self-powdered aptasensor with a metal-ligand charge transfer (MLCT)-induced signal-off strategy was established for microcystin-LR (MC-LR) sensing. The aptasensor was based on a self-breathing-like dual photoelectrode photocatalytic fuel cell (PFC) that was assembled with visible-light responsive ternary NG-TiO2-Ag and NG-BiOBr nanocomposites as photoelectrodes. The device did not require aeration or a membrane in a single-compartment cell. The self-powdered PFC system exhibited a greater power output than previously-reported ones that used only TiO2. The photo-triggered self-bias between the photoelectrodes generated electron transfer and a power output in the external circuit. A self-powered aptasensor for MC-LR was constructed using an MC-LR-binding aptamer as the recognition element. The results showed an unexpected sequential decrease in power output, followed by the capture of MC-LR, which is different from earlier signal-on strategies. The inhibited output of the PFC after MC-LR capture was controlled by an MLCT-induced signal-off mechanism, which was confirmed by the UV-Vis absorption and fluorescence emission spectra. Furthermore, the power output of the self-powdered sensor depended on the MC-LR concentration. When used for ultrasensitive trace MC-LR detection, the self-powdered sensor showed a linear relationship from 1 pM to 316 nM and a detection limit of 0.33 pM. This work provides theoretical guidance for sensing strategies using self-powdered sensors and offers a rational device design for cost-effective electricity generation from renewable resources.

DNA methylation catalyzed by M.SssI methyltransferases (MTase) has important roles in gene expression and other cellular activities, and relates to some diseases, especially cancers. Therefore, it is important to develop a sensitive sensing platform for M.SssI MTase activity assay. Here, taking zeolitic imidazolate framework-8 (ZIF-8) polyhedra as the carriers of graphene quantum dots (GQDs), GQDs-embedded ZIF-8 polyhedra (denoted as GQDs@ZIF-8 polyhedra) were successfully prepared and used as the multi-functional signal quencher to construct a novel signal-off photoelectrochemical (PEC) biosensor for M.SssI MTase activity assay. Firstly, the indium tin oxide (ITO) slice was modified with TiO2, poly(diallyldimethylammonium chloride) and CdTe quantum dots (QDs). The obtained electrode was used as the photoelectrode and labeled as ITO/TiO2/CdTe QDs. Then, single-stranded DNA (S1) was anchored on the photoelectrode surface via S-Cd bond. After hybridization between S1 and biotinylated single-stranded DNA (S2), the streptavidin (SA)-labeled GQDs@ZIF-8 polyhedra were introduced to the modified electrode via the specific reaction between biotin and SA. As the signal quencher, GQDs@ZIF-8 polyhedra could not only inhibit the photocurrent signal of the ITO/TiO2/CdTe QDs electrode due to the steric hindrance effect, but also act as peroxidase mimetics to catalyze precipitation reaction of 4-chloro-1-naphthol, resulting in the evident depression of the photocurrent signal. For the specially designed S1/S2 double-strand DNA, the decreased photocurrent was quantitatively correlated with the M.SssI MTase activity (linear response range, 0.005-150 U mL-1; detection limit, 0.004 U mL-1). The developed GQDs@ZIF-8 polyhedra and related PEC biosensor may have potential applications in clinical research and disease diagnosis.

A fluorescent probe is described for detection of mercury(II) ion by using L-cysteine-modified gold nanoparticles (Cys-AuNP). These were fabricated by a tube-based redox reaction where Cys acts as both the reducing reagent and capping ligand. The Cys-AuNP display red fluorescence, with excitation/emission peaks at 373/625 nm. Owing to the high-affinity of the Hg(II)-Au(I) interaction and the Hg(II)/carboxy or amino group interaction, the presence of Hg(II) cause selective quenching the fluorescence, while other metal ions do not give such an effect. Based on these findings, a method was designed for the determination of Hg(II) that has attractive figures of merit. These include a low limit of detection (1.3 nM), a wide detection range (from 2 nM to 30µM), and excellent specificity. The method was applied to Hg(II) screening in (spiked) tap and river water, and it gave satisfactory results. Graphical abstract Schematic representation of the application of L-cysteine modified gold nanoparticles (Cys-AuNP) for qualitative and quantitative detection of mercury(II) ions. Based on the interaction between Cys-AuNP and mercury(II) ion to quench the red fluorescence of Cys-AuNP, the target mercury(II) can in turn be determined by a fluorometric method.

An aptamer based assay is described for the determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework-graphene composite of type UiO-67/GR is used as the substrate, and an aptamer-gold nanoparticles-horseradish peroxidase (Apt-AuNP-HRP) conjugate the signal amplification probe. A phosphate-terminal and partially complementary DNA (cDNA) of the aptamer is covalently bound to UiO-67/GR via the chemical complexation between phosphate and Zr-OH groups of UiO-67, and then S. typhimurium and cDNA will compete for the binding sites. The binding of Apt-AuNP-HRP to S.typhimurium leads to the formation of strong conjugates. The unbound signal probes then attach to the surface of a glassy carbon electrode via hybridization with cDNA. This generates a large current response (best measured at a potential as low as -0.02 V vs. saturated calomel electrode) under the catalytic action of HRP on the H2O2-hydroquinone system. Under the optimal conditions, the differential pulse voltammetric signal decreases linearly in the 2 × 101 - 2 × 108 cfu·mL-1 S.typhimurium concentration range, with a lower detection limit of 5 cfu·mL-1 (based on S/N = 3). The method was successfully applied to the detection of S. typhimurium in spiked milk samples. Graphical abstract Schematic presentation of electrochemical determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework (type UiO-67) and graphene (GR) composite were used as substrate, and gold nanoparticles carrying horseradish peroxidase (HRP) for signal amplification. HQ: hydroquinone; cDNA: complementary DNA of aptamer.

Herein, a novel signal-off photoelectrochemical (PEC) aptasensor was proposed for sensitive detection of thrombin on the basis of C60@C3N4 nanocomposites as quencher and Au nanoparticles (depAu) decorated perylene tetracarboxylic acid (PTCA) as sensing platform. Owing to the excellent membrane-forming of PTCA and superior conductivity of depAu, the PTCA between two depAu layers can simply and effectively produce an extremely high initial photocurrent to afford a precondition for sensitive biodetection. Thereafter, the assembly of C60@C3N4 nanocomposites on electrode via typical sandwich reaction enabled the generation of a significantly decreased photocurrent. Here, the C3N4 with high surface area not only provided massive binding sites for C60 immobilization, but also partly competed with PTCA in light absorption for producing a significantly smaller photocurrent in the presence of electron donor ascorbic acid (AA). Additionally, both the C3N4 and C60 have the poor conductivity, which could inhibit the electron transfer to achieve a further decreased photocurrent, effectively improving the sensitivity of proposed biosensor. As a result, the PEC biosensor in a \"signal-off\" mode showed an extremely low detection limit down to 1.5 fM, providing a sensitive and universal strategy for protein detection.

We developed a novel \"signal-off\" photoelectrochemical (PEC) aptasensor based on an aptamer bridged DNA network structure for the sensitive detection of vascular endothelial growth factor (VEGF165), using g-C3N4 as photoactive material. The DNA network provides an excellent platform for the immobilization of methylene blue (MB), which can facilitate the electron transport through the DNA helix structure and suppress the recombination of electron-hole pairs generated by g-C3N4. In the presence of the target VEGF165, the DNA network can be destroyed adequately by the recognition between VEGF165 and the aptamer, resulting in the release of MB. Therefore, the originally enhanced electron transfer process could be inhibited, leading to a remarkable decrease of the photocurrent. A good linear relationship between the PEC signal and the logarithm of VEGF165 concentration over the range of 100fM to 10nM with a detection limit of 30 fM can be obtained. Our concept can be easily extended to develop aptasensors for the sensitive detection of different targets by triggering the release of the payloads from their corresponding aptamer bridged DNA networks.