Enzyme-free signal amplified Au nanoparticle fluorescence detection of thrombin via target-triggered catalytic hairpin assembly

PEC thrombin aptasensor based on Ag-Ag2S decorated hematite photoanode with signal-down effect of precipitation catalyzed by G-quadruplexes/hemin

A photoelectrochemical (PEC) aptasensor for thrombin detection was rationally designed based on the photoanode of one-dimensional hematite nanorods (α-Fe₂O₃ NRs) with several steps of modifications. Uniform α-Fe₂O₃ NRs were grown vertically on the surface of fluorine-doped tin oxide (FTO) conductive glass through a one-step hydrothermal method; then Ag was grown on the surface of α-Fe₂O₃ NRs through a photoreduction method followed by a partial in-situ transformation into Ag₂S, conferring an improvement on the initial photocurrent. Two main critical factors, namely, the steric hindrance of thrombin, benzoquinone (BQ) precipitation oxidized by H₂O₂ under the catalysis of G-quadruplexes/hemin, contributed to the sensitive signal-down response toward the target. Photocurrent signals related with thrombin concentration was established for thrombin analysis due to the non-conductive complex as well as their competitive consumption of electron donors and irradiation light. The excellent initial photocurrent was combined with the signal-down amplification in the design of the biosensor, conferring a limit of detection (LOD) as low as 40.2 fM and a wide linear range from 0.0001 nM to 50 nM for the detection of thrombin. The proposed biosensor was also assessed in terms of selectivity, stability, and applicability in human serum analyses, which provided an appealing maneuver for the specific analysis of thrombin in trace amount.

Gold nanoparticle-based signal amplified electrochemiluminescence for biosensing applications

Since the content levels of biomarkers at the early stage of many diseases are generally lower than the detection threshold concentration, achieving ultrasensitive and accurate detection of these biomarkers is still one of the major goals in bio-analysis. To achieve ultrasensitive and reliable bioassay, it requires developing highly sensitive biosensors. Among all kinds of biosensors, electrogenerated chemiluminescence (ECL) based biosensors have attracted enormous attention due to their excellent properties. In order to improve the performance of ECL biosensors, gold nanoparticles (Au NPs) have been widely utilized as signal amplification tags. The introduction of Au NPs could dramatically enhance the performance of the constructed ECL biosensors via diverse ways such as electrode modification material, efficient energy acceptor in ECL resonant energy transfer (ECL-RET), reaction catalyst, surface plasmon resonance (SPR) enhancer, and as nanocarrier. Herein, we summarize recent developments and progress of ECL biosensors based on Au NPs signal amplification strategies. We will cover ECL applications of Au NPs as a signal amplification tag in the detection of proteins, metal ions, nucleic acids, small molecules, living cells, exosomes, and cell imaging. Finally, brief summary and future outlooks of this field will be presented.

A sensitive electrochemiluminescent sensor chip based on ssDNA-Ru (II) complex and aptamer for the determination of thrombin

In this work, an electrochemiluminescence (ECL) sensor chip for sensitive detection of thrombin (TB) was prepared using a screen-printed electrode (SPE) as a working electrode and an aptamer as a specific recognition moiety. To produce an ECL sensor chip, a layer of pL-Cys was immobilized on the surface of SPE by the cyclic voltammetry scanning method, a layer of AuNPs was assembled through an Au-S bond and hairpin DNA was further immobilized on the electrode surface. Ru (bpy)₂ (mcpbpy)²⁺ , as a luminescent reagent, was covalently bound to ssDNA to prepare a luminescent probe ssDNA-Ru. The probe hybridized with TB aptamer to form a capture probe. In the presence of TB, the TB aptamer in the capture probe bound to TB, causing the release of ssDNA-Ru that could bind to hairpin DNA on the electrode surface. Ru (II) complex as a luminescent reagent was assembled onto the electrode, and pL-Cys was used as a co-reactant to. enhance the ECL efficiency. The ECL signal of the sensor chip generated based on the above principles had a linear relationship with log TB concentration at a range of 10 fM-1 nM, and the detection limit was 0.2 fM. Finally, TB detection by this method was verified using real blood samples. This work provides a new method using an aptamer as a foundation and SPE as a material for the detection of biological substances.

Efficient detection for Nitrofurazone based on novel Ag2S QDs/g-C3N4 fluorescent probe

In the paper, a novel fluorescent probe based on Ag₂S QDs/g-C₃N₄ composite was synthesized by loading Ag₂S quantum dots (Ag₂S QDs) on the surface of g-C₃N₄ through in-situ synthesis method and developed to detect Nitrofurazone (NFZ) sensitively. The results showed that the linear detection range of Ag₂S QDs/g-C₃N₄ to NFZ was 0-30 μM, with a low detection limit of 0.054 μM. The results of time-fluorescence-resolved spectroscopy and UV-vis absorption spectroscopy exhibited that the possible detection mechanism of Ag₂S QDs/g-C₃N₄ to NFZ was proposed to be Internal Filtration Effect (IFE). Moreover, Multiwfn wavefunction analysis was employed to uncover the possible interaction between the Ag₂S QDs/g-C₃N₄ and NFZ, thereby further revealing the fluorescence detection mechanism from the scale of atoms. Combining experiments and theoretical calculations, we proposed the sensing mechanism of the formation of non-fluorescent ground state complex linked by hydrogen bonds. This work indicated that the Ag₂S QDs/g-C₃N₄ composite processed the ability to detect NFZ efficiently and sensitively.

A Fluorescence Kinetic-Based Aptasensor Employing Stilbene Isomerization for Detection of Thrombin

It is important to detect thrombin due to its physiological and pathological roles, where rapid and simple analytical approaches are needed. In this study, an aptasensor based on fluorescence attenuation kinetics for the detection of thrombin is presented, which incorporates the features of stilbene and aptamer. We designed and synthesized an aptasensor by one-step coupling of stilbene compound and aptamer, which employed the adaptive binding of the aptamer with thrombin to cause a change in stilbene fluorescence attenuation kinetics. The sensor realized detection of thrombin by monitoring the variation in apparent fluorescence attenuation rate constant (k_app), which could be further used for probing of enzyme–aptamer binding. In comprehensive studies, the developed aptasensor presented satisfactory performance on repeatability, specificity, and regeneration capacity, which realized rapid sensing (10 s) with a limit of detection (LOD) of 0.205 μM. The strategy was successful across seven variants of thrombin aptasensors, with tunable k_app depending on the SITS (4-Acetamido-4′-isothiocyanato-2,2′-stilbenedisulfonic acid disodium salt hydrate) grafting site. Analyte detection mode was demonstrated in diluted serum, requiring no separation or washing steps. The new sensing mode for thrombin detection paves a way for high-throughput kinetic-based sensors for exploiting aptamers targeted at clinically relevant proteins.

Dual-recognition colorimetric sensing of thrombin based on surface-imprinted aptamer-Fe3O4

Thrombin plays an essential role in blood coagulation and some physiological and pathological processes. The convenient, rapid, sensitive, and specific detection of thrombin is of great significance in clinical research and diagnosis. Herein, surface molecularly imprinted polymer (MIP) was modified on aptamer-functionalized Fe3O4 nanoparticles (MIP-aptamer-Fe3O4 NP) for thrombin colorimetric assay by taking advantage of the peroxidase-like activity of Fe3O4 NP. With the adsorption of thrombin into imprinted cavities, the exposed surface area of Fe3O4 NP decreased, causing a decrease in its peroxidase-like activity toward 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. On the other hand, the reductive amino acids on the thrombin surface also impeded the oxidation of TMB. Both phenomena caused the light blue color of the sensing solution. Thus, a specifically sensitive colorimetric approach for the visual detection of thrombin was proposed with a linear range and limit of detection of 108.1 pmol L-1-2.7 × 10-5 mol L-1 and 27.8 pmol L-1, respectively. Moreover, due to the double recognition elements of MIP and aptamer, the prepared MIP-aptamer-Fe3O4 NP showed higher selectivity to thrombin than that based on only one recognition element. It is worth noting that no special property (e.g. electrochemical or fluorescence activity) of the template was required in this work. Thus, more template molecules can be easily, selectively, and sensitively detected based on the proposed MIP-aptamer-mimic enzyme colorimetric sensing strategy.