Signal Off Research Articles

Peptide-Based Biosensor with a Luminescent Copper-Based Metal-Organic Framework as an Electrochemiluminescence Emitter for Trypsin Assay.

A copper-based metal-organic framework (JUC-1000) has emerged as a promising electrochemiluminescence (ECL) emitter in the domains of bioanalysis and immunoassay. Herein, a highly efficient signal "on-off" peptide-based biosensor was constructed for trypsin (TPN) assay. JUC-1000 synthesized using an organic ligand of H4BDPO was functionalized as the ECL emitter, whose cathodic ECL behavior in aqueous media was first investigated using potassium persulfate (K2S2O8) as the coreactant. To further amplify the ECL signal, highly catalytic Ag@CeO2 nanoparticles were fabricated as both a substrate and an coreaction accelerator, which can efficiently catalyze the reduction of S2O82- to generate more sulfate anion radicals (SO4•-) for ECL enhancement, thereby generating strong and stable ECL signals in a "signal on" state. The functionalized JUC-1000 emitter was connected to the Ag@CeO2 sensing layer though a heptapeptide (HWRGWVC, HGC), and TPN as the target can specifically cleave the carboxyl side of arginine residues in HGC, leading to the release of emitters in a "signal off" state. Based on the efficient signal-switching, the biosensor exhibited linear ECL responses to the added TPN concentration, realizing sensitive detection of TPN in 10 fg/mL to 100 ng/mL with a limit of detection of 3.46 fg/mL. This work proposed an attractive orientation for the fundamental research of applying transition metal-organic frameworks as ECL emitters in bioanalysis and immunoassay.

Porphyrin-Based Covalent Organic Framework Thin Films as Cathodic Materials for “On–Off–On” Photoelectrochemical Sensing of Lead Ions

Currently, cathodic photoelectrochemical (PEC) sensors, which could effectively reduce background interference, are urgently required for ultrasensitive environmental monitoring. Herein, porphyrin-based covalent organic framework (TAPP-COF) thin films were fabricated via a bottom-up growth approach on the liquid/liquid interface and applied as a photocathode material to "on-off-on" PEC sensing of Pb2+. Benefitting from the unique charge channels of COFs and the good photoelectric properties of porphyrin, the as-prepared TAPP-COF thin films presented an improved photocathodic current, with a strongly enhanced "signal-on" response with low background. Then, CdSe@SiO2 quantum dots (QDs), as a quenching agent, were introduced through a hybridization chain reaction (HCR) to obtain a "signal off" PEC response. Afterward, with the introduction of target Pb2+, CdSe@SiO2 QDs were detached from TAPP-COF thin films, and the PEC response transformed into a signal-on state. Benefiting from the multiple-quenching and steric hindrance effect of CdSe@SiO2 QDs and the photocathodic property of TAPP-COFs, accurate monitoring of Pb2+ in a wide detection range from 0.05 to 1000 nM with a lower detection limit of 0.012 nM was realized based on the proposed on-off-on PEC approach. Notably, the methodology provides an efficient platform for ultrasensitive determination of heavy metal ions, which would play a significant role in environmental monitoring and public safety fields.

A Multiplexed Self-Powered Dual-Photoelectrode Biosensor for Detecting Dual Analytes Based on an Electron-Transfer-Regulated Conversion Strategy.

Due to the inherent mechanism limitation of photocatalytic fuel cell based self-powered biosensors (PFC-SPBs), it was difficult to distinguish the power density of various photoactive materials or recognition events in one detection process, which made it lack multitarget quantitative capacity. In order to solve this problem, we proposed an electron-transfer-regulated conversion strategy for the construction of multiplexed PFC-SPBs. Herein, the n-type CdS/Fe2O3 nanorod array (NR) heterojunction and p-type CuBr semiconductor were used as photoactive materials to prepare the photoanode and photocathode. Based on the appropriate Fermi level differentiation between these two photoelectrodes, a self-powered sensing platform driven by visible light without external energy supply was achieved. In this design, two kinds of common and easily coexisting mycotoxins OTA and AFB1 acted as model analytes. The coupling of "signal off" and "signal on" was realized by controlling the electronic transmission on the interface between the photoanode and photocathode, so as to achieve the simultaneous detection of two mycotoxins. This work established a proof-of-concept for the integration of a dual-photoelectrode with dual-assay that could provide the innovative inspiration for the formation of a general multiplexed self-powered sensing platform.

Self-Assembly of Gold Nanoclusters into a Metal-Organic Framework with Efficient Electrochemiluminescence and Their Application for Sensitive Detection of Rutin.

Ligand-protected gold nanoclusters (Au NCs) are promising electrochemiluminescence (ECL) emitters because of their striking optical properties and excellent biocompatibility, but free vibration and rotation of their ligand result in low ECL efficiency, dramatically limiting their applications. Herein, using the ligand of Au NCs as one of the building units, a Au NC-based metal-organic framework (Au NC-based MOF) was constructed by the coordination-assisted self-assembly strategy, which not only impedes the ligand rotation-induced energy dissipation but also diminishes the self-quenching effect due to the spatial distribution of Au NCs. As a proof of concept, the prepared GSH-Au NCs@ZIF-8 gives rise to a 10-fold enhanced anodic ECL efficiency compared to that of densely aggregated GSH-Au NCs with triethylamine as the coreactant. Based on high ECL efficiency of GSH-Au NCs@ZIF-8, a "signal off" sensing platform was proposed with rutin as a model analyte, achieving a low detection limit of 10 nM. Therefore, the strategy paves an effective and alternative methodology to enhance ECL efficiency of metal NCs, considerably broadening their potential applications in sensing analysis, clinical diagnosis, and light-emitting devices.

An “on-off” electrochemiluminescence immunosensor for PIVKA-II detection based on the dual quenching of CeO2–Au-g-C3N4 hybrids by Ag nanocubes-VB2

Herein, we report a novel dual-quenching electrochemiluminescence (ECL) immunosensor for detecting protein induced by vitamin K absence or antagonist-II (PIVKA-II) based on ECL resonance energy transfer (ECL-RET). In this protocol, self-accelerated ECL hybrids of CeO2 and Au nanoparticles functionalized g-C3N4 nanosheets (CeO2–Au-g-C3N4) were prepared, which exhibited high ECL emission in the presence of S2O82− as a coreactant for “signal on” state. Concretely, CeO2 with a reproducible redox couple of Ce3+ and Ce4+ could act as an efficient co-reaction accelerator to generate more oxidizing intermediate (SO4•−) to significantly self-promote the ECL emission of g-C3N4 NSs/S2O82− ECL system. Besides, Au nanoparticles not only accelerated electron transfer in the ECL process, but also provided massive active sites for biomolecules immobilization. The dual quenching labels of Ag nanocubes modified with vitamin B2 (AgNCs-VB2) were firstly proposed towards g-C3N4 NSs/S2O82− ECL system by ECL-RET, resulting in the remarkable ECL decrease for “signal off” state. Based on the sandwich immunoreaction, the “on-off” PIVKA-II ECL immunosensor gratifyingly possessed excellent detection sensitivity with the linear range of 0.4 pg mL−1–10 ng mL−1 and the low detection limit of 28.46 fg mL−1 (S/N = 3). This presented strategy might provide a potential alternative tool for PIVKA-II detection in medical research and early clinical diagnostics of hepatocellular carcinoma.

Electrochemical detection of alkaline phosphatase activity through enzyme-catalyzed reaction using aminoferrocene as an electroactive probe.

As a nonspecific phosphomonoesterase, alkaline phosphatase (ALP) plays a pivotal role in tissue mineralization and osteogenesis which is an important biomarker for the clinical diagnosis of bone and hepatobiliary diseases. Herein, we described a novel electrochemical method that used aminoferrocene (AFC) as an electroactive probe for the ALP activity detection. In the condition with imidazole and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC), the AFC probe could be directly labeled on single-stranded DNA (ssDNA) by one-step conjugation. Specifically, thiolated ssDNA at 3'-terminals was modified to the electrode surface through Au-S bond. In the condition without ALP, AFC could be labeled on ssDNA by conjugating with phosphate groups. In the presence of ALP, phosphate groups were catalyzed to be removed from the 5'-terminal of ssDNA. The AFC probe cannot be labeled on ssDNA. Thus, the electrochemical detection of ALP activity was achieved. Under optimal conditions, the strategy presented a good linear relationship between current intensity and ALP concentration in the range of 20 to 100mU/mL with the limit of detection (LOD) of 1.48mU/mL. More importantly, the approach rendered high selectivity and satisfactory applicability for ALP activity detection. In addition, this method has merits of ease of operation, low cost, and environmental friendliness. Thus, this strategy presents great potential for ALP activity detection in practical applications. An easy, sensitive and reliable strategy was developed for the detection of alkaline phosphatase activity via electrochemical "Signal off".

Novel Porphyrin Zr Metal-Organic Framework (PCN-224)-Based Ultrastable Electrochemiluminescence System for PEDV Sensing.

The sensitive detection of coronavirus is of vital importance for the prevention of its rapid spread. Porcine epidemic diarrhea virus (PEDV) is a highly contagious coronavirus that causes severe diarrhea and death in neonatal piglets. In this work, a novel PCN-224-based electrochemiluminescence (ECL) system was constructed for PEDV detection with high sensitivity. We found that PCN-224 can be employed as an ECL reporter with a strong signal because of its zirconium-based organic porous frame nanomaterial with a large specific surface area and stable structure. TiO2 nanoparticles were used as an accelerator for the first time to promote the reduction of coreactant potassium peroxydisulfate on the cathode; thus, the initial ECL signal of PCN-224 was significantly amplified. In the presence of PEDV, the ECL signal decreased due to the block effect to electron transfer. As a result, the novel "signal off" biosensor achieved a sensitive detection of PEDV ranging from 1 pg/mL to 10 ng/mL, with a detection limit of 0.4 pg/mL (S/N = 3). Importantly, the PCN-224 nanomaterial enriched the ECL system in biological analysis, and the proposed strategy provided a new route for coronavirus detection.

A "signal off" aptasensor based on NiFe2O4 NTs and Au@Pt NRs for the detection of deoxynivalenol via voltammetry.

A "signal off" aptasensor has been developedto detect deoxynivalenol (DON). DON aptamers (Apt) were used as biological recognition elements, nickel ferrite nanotubes (NiFe2O4 NTs) are used as the base material to increase the surface area of the electrode, and the Au@Pt NRs were used as carriers for loading signal labels thionine (Thi) and complementary strand (cDNA). In the presence ofDON itwill be specifically captured by Apt, then the competition mechanism was triggered; the signal molecules fall off from the electrode surface, which then causes the electrode signal to decrease. NiFe2O4 NTs and Au@Pt NRs were characterized by transmission electron microscope (TEM), scanning electron micrograph (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The designed sensor providesaconcentration range of 1 × 10-8 to 5 × 10-4mgmL-1andlimit of detection of3.02 × 10-9mgmL-1. Determination ofDON in corn meal samples was investigatedand the recovery was 98.4 to 103.5%. The proposed aptasensor displayed good sensitivity, high specificity, and acceptable reproducibility. Graphical abstract Based on NiFe2O4 NTs as substrate material and Au@Pt NRs as signal label prepared DON aptasensor for the determination of DON.

110 kV substation relay protection

In this paper, the main electric wiring mode of 110kV substation is selected, the structure of substation is determined, and then the main wiring diagram is drawn. According to the design and load of the primary electrical connection, select the maximum and minimum operating modes to calculate the short circuit separately. Then, according to the short-circuit current parameters, the relay protection of transmission lines, transformers, busbars, etc. is set, and the configured protections include current quick-break protection, gas protection, and longitudinal differential protection. Finally, a comprehensive evaluation of the selected protection devices is carried out. Adding relay protection device in substation can send out fault signal and cut off fault line in time to reduce the occurrence of substation fault, so as to ensure the reliable power supply of users and enterprises.

A novel ultrasensitive photoelectrochemical biosensor for detecting microRNA 21 based on cosensitization strategy and p-n heterojunction quenching mode

Highly sensitive detection of biomarkers has a vital role in clinical diagnosis and disease treatment. Integrating cosensitization strategy and p-n heterojunction quenching mode, we have established a novel ultrasensitive “signal off” photoelectrochemical (PEC) biosensor for detecting microRNA 21 (miRNA 21) via target-triggered catalytic hairpin assembly (CHA) cycling amplification. The n-type nano-hybrid (Bi2S3-ZnS) wrapped by toluidine blue O dye (TBO@Bi2S3-ZnS composite) has been synthesized, in which TBO and Bi2S3 as photosensitizers for photoactive matrix of ZnS. Since the cosensitization effect of Bi2S3 and TBO, 136-fold enhancement in PEC signal of TBO@Bi2S3-ZnS has been acquired compared with ZnS. Trace miRNA 21 can be transformed to abundant p-type copper sulfide (CuS) labeled signal tags to form p-n heterojunction with TBO@Bi2S3-ZnS, leading to obvious quenching effect. Thus, the PEC signals decrease with the increasing concentration of miRNA 21 and achieve the quantitative detection. The proposed PEC biosensor exhibits good linear relationship to miRNA 21 ranging from 1.0 × 10−17 to 1.0 × 10−11 mol·L−1 with a limit of detection of 3.3 × 10−18 mol·L−1. This biosensor based on TBO used as photosensitizer for the first time may offer new opportunities for detecting other biomarkers and facilitate the application of organic dyes in PEC sensing field.

An orbitron-like 3D DNA clip-based nanomachine and its application for sensitive fluorescent bioassay of MicroRNA

Herein, an orbitron-like three-dimensional (3D) DNA clip-based nanomachine was proposed for ultrasensitive fluorescent bioassay of microRNA, which was constructed by mechanically interlocking double-DNA-ring with two single-stranded DNAs, performing an orbitron-like 3D structure with double freely rotated DNA rings as the open state. In the presence of target microRNA, the proposed orbitron-like 3D DNA clip can alter its structure from open to closed state in identification of the target microRNA, generating the closure between the previously modified fluorescent dyes and the quenchers to perform a “signal off” fluorescent signal correlated with the concentration of target microRNA. Compared with the normal DNA nanomachines, such as DNA tweezers constructed by self-assembly of three single-stranded DNAs which regulated the open and closed states on the basis of linear conformational changes, the proposed 3D DNA clip-based nanomachine with high mechanical rigidity realized the conformational changes in 3D space with the assistance of target microRNA, which could effectively increase the adjustable distance range and reduce the background signal. Furthermore, the 3D DNA clip-based nanomachine was applied in the fluorescent detection of microRNA-21 with favorable performances for the sensitive detection of microRNA in cells, providing a new avenue for early clinical diagnoses of disease.

Glycosaminoglycan‐Induced Emissive J‐Aggregate Formation in a meso‐Ester BODIPY Dye

AbstractThe analyte‐directed formation of emissive J‐aggregates of a meso‐ester BODIPY dye is explored in the design of fluorescence “light‐up” probes. The heparin‐specific pyridinium‐functionalized meso‐ester BODIPY dye C10‐Py+ self‐assembles in aqueous buffer into spherical aggregated nanostructures with spectroscopic features indistinguishable from the monomeric dye (signal off). In the presence of heparin, the aggregated assemblies rearrange and associate with heparin through charge‐pairing interactions, triggering the spontaneous formation of emissive J‐type aggregates (signal on). The heparin‐induced J‐aggregate formation of C10‐Py+ provides an excellent “turn‐on” signal with large spectral shifts. The response is highly selective for heparin over other closely related glycosaminoglycan (GAG) analogues, sensitive, fast, and operationally simple. Assays for heparin in human serum, and for the adulterant OSCS in heparin are demonstrated, confirming the reliability and robustness of the J‐aggregation approach using meso‐ester BODIPY dyes in the design of aggregation‐induced emission (AIE)‐based fluorogenic probes.

Dual-modal label-free genosensor based on hemoglobin@gold nanocluster stabilized graphene nanosheets for the electrochemical detection of BCR/ABL fusion gene

For the first time, we have successfully synthesized stable graphene nanosheets from graphite powder through sonication in the hemoglobin-capped gold nanoclusters (Hb@AuNCs) solution for biosensing application. This approach, as a simple method for the exfoliation and fragmentation of graphite in a nanocluster solution, enabled us to produce stable aqueous graphene dispersions at low cost and without the need for hazardous chemicals or tedious experimental procedures. In this method, Hb@AuNCs were used not only as stabilizing agent of graphene through non-covalent bonding, but also as dispersing agent of few-layer graphene nanosheets. The Hb@AuNCs stabilized graphene (Hb@AuNCs-G) was characterized by high resolution transmission electron microscopy (HRTEM), zeta-sizer and Raman spectroscopy. Then, the graphene nanosheets were applied as a novel versatile electrochemical platform for ultrasensitive biosensing of short DNA species of chronic myelogenous leukemia (CML) based on the “signal off” and “signal on” strategies. For this purpose, a single strand DNA (ssDNA) was immobilized on the Hb@AuNCs-G/AuNPs modified electrode surface and acted as the biorecognition element. Methylene blue (MB), as the signaling probe, was then intercalated into the ssDNA. The intercalated MB was liberated upon interaction with the synthetic complementary DNA (cDNA, target), thereby resulting in the apparent reduction of MB redox signal. This designed “signal off” sensing system enabled the voltammetric determination of the target cDNA over a dynamic linear range (DLR) of 0.1 fM to 10 pM with a limit of detection (LOD) of 0.037 fM. In the “signal on” strategy, the response to the cDNA was detected by monitoring the change in the electron transfer resistance (Rct) using the ferro/ferricyanide system as a redox probe. The charge transfer resistance of the probe was found to increase linearly with increasing concentration of target cDNA in the range of 0.1 fM–10 pM with a limit of detection of 0.030 fM. Finally, the selectivity and feasibility of genosensor was evaluated by the analysis of derived nucleotides from mismatched sequences and the clinical samples of patients with leukemia as real samples, respectively.

A novel electrochemiluminescence biosensor based on the self-ECL emission of conjugated polymer dots for lead ion detection.

The poly[(9,9-dioctylfuorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT) was carboxyl-functionalized to prepare polymer dots (C-PFBT Pdots), which served as a self-ECL emitter for producing an extraordinary ECL signal without any exogenous coreactants. The C-PFBT Pdots-modified electrode captured the substrate DNA and further hybridized with a ferrocene (Fc)-labeled DNA. The ECL emission of C-PFBT Pdots was quenched by Fc (a signal off state). After the DNAzyme was added, the DNAzyme-substrate hybrids were formed through hybridizing between DNAzyme and substrate and the Fc-labeled DNA was released. In the presence of target Pb2+, the DNAzyme-substrate hybrids could be specifically recognized and cleaved to release the DNAzyme and Pb2+. Ultimately, the released DNAzyme would further hybridize with the substrate for producing the DNAzyme-substrate hybrids and then were cleaved by the released Pb2+. As a result, the DNA walking machine was generated and the substantial Fc was away from C-PFBT Pdots to obtain a signal on state. Such a strategy achieved a sensitive detection of Pb2+ and the detection limit was as low as 0.17pM. Moreover, making this ECL biosensor for an intracellular Pb2+ detecting, a convincing performance was achieved. The self-ECL emitter C-PFBT Pdots combining with the quencher Fc provided a new strategy and platform for constructing a coreactant-free ECL assay.

Photoelectrochemical Immunosensor Based on ZnIn2S4/Bi2Se3 Nanocomposite for the Determination of Cardiac Troponin I

In this work, a novel flexible photoelectrochemical immunosensor is developed to determine cardiac troponin I (cTnI) in serum. The flower-like ZnIn2S4 nanospheres (ZIS), as signal amplification material, were successfully synthesized by a solvothermal method. The ZIS and Bi2Se3 were modified on the indium tin oxide- polyethylene terephthalate (ITO-PET) electrode, which effectively accelerates the electronic transition and improved the photocurrent conversion efficiency (signal on). However, the binding of antigen–antibody proteins blocks the electron transfer, resulting in a greatly reduced photocurrent (signal off). By adding the second antibody modified by CdSe quantum dots (CdSe QDs-Ab2), the photocurrent is increased (signal on). The constructed immunosensor has a linear range from 0.08 to 40 ng/mL with a detection limit of 0.026 ng/mL, which shows excellent selectivity, high sensitivity, and good stability. The photoelectrochemical immunosensor has broad application prospects for the clinical examination of myocardial infarction.

A versatile dendritical amplification photoelectric biosensing platform based on Bi2S3 nanorods and a perylene-based polymer for signal "on" and "off" double detection of DNA.

A novel versatile dendritical amplification photoelectric (PEC) biosensing platform using Bi2S3 nanorods and perylene-based polymer (PTC-NH2) as double signal probes is proposed for the detection of trace target DNA. Bi2S3 nanorods as efficient photoactive materials were firstly immobilized on the Au nanoparticle (NP) modified electrode and generated a high PEC signal. Exonuclease III (Exo III)-assisted target recycling generated a large number of DNA product chains (PC), PC hybridized with hairpin DNA (H1) on AuNPs/Bi2S3/ITO, and then triggered rolling circle amplification (RCA) and the hybridization chain reaction (HCR) to form the dendritic structure with abundant DNA duplexes. After large amounts of Mn(iii) meso-tetra(N-methyi-4-pyridyl)porphine pentachloride (MnPP) were embedded in the dendritic structure, they efficiently quenched the PEC signal, realizing the "signal off" detection of the target. In addition, the dendritic structure was also formed on AuNPs/ITO, and large amounts of PTC-NH2 molecules as the PEC probe were inserted into the dendritic structure, achieving a highly enhanced PEC current for the "signal on" detection of the target. This biosensing platform with double signals exhibits good analytical performance with wide linear ranges. This study develops a new DNA nanostructure-amplified versatile PEC sensing platform for bioanalysis, with promising potential for application in gene therapy and clinical analysis.

Peptide cleavage-mediated photoelectrochemical signal on-off via CuS electronic extinguisher for PSA detection

In this work, a peptide-based photoelectrochemical (PEC) biosensor was constructed based on CdTe/TiO2 sensitized structure as electrode and CuS nanocrystals as signal amplifier for the ultrasensitive detection of protein. After peptide was fixed to the CdTe/TiO2 electrode surface, the double-helix DNA (dsDNA) was immobilized at the end of the peptide and used as a carrier to immobilize the doxorubicin-copper sulfide nanocrystals (Dox-CuS) conjugates. As a proof of concept, prostate specific antigen (PSA) has been chosen as the model. In absence of PSA, CuS nanocrystals could consume electron donors and exciting light energy. Additionally, the steric hindrance effect of biomacromolecules hindered the movement of electron donors to the photoelectrode. Eventually, the photoelectric response signal was reduced, and the biosensor was in a "signal off" state. When PSA existed, the PSA specifically cleaved the peptide, and DNA/Dox-CuS probes were released from the electrode surface, resulting in a "signal on" state. The PEC biosensor revealed good specificity, stability, and reproducibility, and it exhibited excellent application in PSA analysis with a linear range from 0.005 to 20ngmL-1 and a low detection limit of 0.0015ngmL-1. This PEC biosensor may have potential applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Ferrocenoyl conjugates of hydroxyl group containing side chain amino acids: Synthesis, electrochemical study and reactivity toward electrophiles

Mono- and disubstituted ferrocenoyl amino acid conjugates having free hydroxyl (OH) group at the amino acid side chain is synthesized, namely Fc–CO–aa-OCH3 (1a, 2a, 3a), and Fc-[CO-aa-OCH3]2 (1b, 2b, 3b), Fc = ferrocene, aa = l-serine (L-Ser, 1), l-tyrosine (L-Tyr, 2), l-threonine (L-Thr, 3). The reactivity of the OH group in 1a toward substitution reaction by acetyl chloride, p-toluene sulfonyl chloride and phosphoric acid is investigated. The resulting compounds are Fc–CO–L-Ser(C(O)–CH3)–OCH3 (1c), Fc–CO–L-Ser(S(O)2–C6H4–CH3)–OCH3 (1d) and Fc–CO–L-Ser(P(O)–(OH)2)–OCH3 (1e). The prepared Fc-amino acid conjugates are fully characterized by standard spectroscopic methods. The cyclic voltammetry of the Fc-compounds show a quasi-reversibility for conjugates 1a-3a (E1/2 = 0.64 V) and for 1b, 3b (E1/2 = 0.85 V), while an irreversible behavior for 2b is observed. The compounds 1c and 1d exhibit quasi-reversibility with E1/2 = 0.71 V, which is shifted anodically by 100 mV compared to the parent conjugate 1a. Fc-conjugate 1e shows complete irreversibility. The study suggests that profound changes in Fc-redox potential is accessible through varying the substituent at the OH group in the amino acid side chain, either by anodic shift of the Fc signal (acylation and tosylation) or turn the signal off by phosphorylation.

Target-driven rolling walker based electrochemical biosensor for ultrasensitive detection of circulating tumor DNA using doxorubicin@tetrahedron-Au tags

In this study, a multiple-legged and highly integrated DNA rolling walker based electrochemical biosensor was developed for ultrasensitive ctDNA analysis through rolling circle amplification (RCA) with doxorubicin@tetrahedron-Au (DOX@TDN-Au) as electrochemical indicator. Upon target-driven RCA, the multiple-legged walker could move along with the predesigned track by strand displacement reactions, resulting in numbers of legs binding irreversibly to iStep probes. The binding of massive legs to iStep probes could effectively impede DOX@TDN-Au tags binding on the surface of sensor and then reached a “signal off” state. Benefiting from the highly amplified efficiency of rolling walker machine and DOX@TDN-Au tags, the established biosensor performed high sensitivity for target detection with a low limit of detection down to 0.29 fM. Moreover, the target ctDNA could hybridize with the ring and capture probe simultaneously, greatly enhancing the specificity of the developed biosensing method. Thus, this biosensing method is a promising tool for detection of ctDNA in the field of clinical diagnostic and tumor progression assessment.

Ratiometric detection of alkaline phosphatase based on aggregation-induced emission enhancement.

Alkaline phosphatase (ALP) is an important enzyme that is associated with many human diseases, so the quantitative detection of ALP is vital from a clinical perspective. Nevertheless, most fluorescent assays for monitoring ALP depend on aggregation-induced quenching (ACQ), single-signal modulation, or a "signal off" mode, which suffer from poor sensitivity, a "false positive" problem, and low signal output. In this work, we utilized the electrostatically driven self-assembly of glutathione-capped gold nanoclusters (GSH-AuNCs, which show aggregation-induced emission, AIE) and amino-modified silicon nanoparticles (SiNPs) to create a hybrid probe (SiNPs@GSH-AuNCs). This nanohybrid probe showed emission from the SiNPs at around 470nm as well as aggregation-induced emission enhancement (AIEE) of the GSH-AuNCs at 580nm. The AIEE of the GSH-AuNCs was quenched in the presence of KMnO4, but the AIEE was recovered by adding ascorbic acid as an oxidation-reduction reaction occurred between KMnO4 and the ascorbic acid. The fluorescence of the SiNPs remained constant whether the AIEE was quenched or not, meaning that the fluorescence of the SiNPs could be used as an internal reference. In a typical enzymatic reaction, ascorbic acid 2-phosphate is hydrolyzed by ALP to produce ascorbic acid. Therefore, the hybrid probe was shown to allow the ratiometric detection of ALP, with a linear range of 0.5-10UL-1 and a limit of detection (LOD) of 0.23UL-1. Finally, the proposed analytical strategy was successfully applied to detect ALP in human serum samples and to determine the concentration of an ALP inhibitor. Graphical Abstract.