Sensitivity Dependence on the Crystal Forms of a Fluorescence Quencher for Silicon Quantum Dots and Its Use in Acetylcholinesterase Assay

Biocompatibility FeOOH QD@ATP-BODIPY nanocomposite for glutathione detection and intracellular imaging

Monitoring of glutathione has attracted considerable attention owing to its biological and clinical significance. An eco-friendly, economic, simple, biocompatible probe with excellent sensitivity and selectivity is very important. Herein, FeOOH QD@ATP-BODIPY nanocomposite was fabricated from one-step synthesized FeOOH quantum dots (FeOOH QD) and commercial boron-dipyrromethene-conjugated adenosine 5'-triphosphate (ATP-BODIPY) for glutathione (GSH) sensing in solutions and living cells. Three fascinate merits of FeOOH QD were confirmed: (a) as fluorescence quencher for ATP-BODIPY, (b) as selective recognizer of GSH and (c) with carrier effects and membrane permeability. The construction and response mechanism of the nanocomposite was based on the competitive coordination chemistry and redox reaction of FeOOH QD between GSH and phosphate group of ATP-BODIPY. Under the optimal conditions, the detection limit for GSH was as low as 68.8 nM. Excellent linear range of 0.2-400 μM was obtained. Furthermore, the chemical response of the nanocomposite exhibits high selectivity toward GSH over other electrolytes and biomolecules. It was successfully applied for GSH determination in human serum samples. The MTT assay exhibited FeOOH QD@ATP-BODIPY nanocomposite own good biocompatibility. FeOOH QD@ATP-BODIPY respond to GSH in living cells in situ was also proved via fluorescence imaging. These suggested that the FeOOH QD@ATP-BODIPY nanocomposite had potential application in biological and clinical applications.

Water in liquid crystal emulsion-based sensing platform for colorimetric detection of organophosphorus pesticide

Development of a simple and convenient method for the rapid detection of organophosphorus pesticides (OPs) is particular important for the safety of environmental water and agriculture products. In this work, the water/liquid crystal (W/LC) emulsion is obtained via dispersing an aqueous solution of sodium dodecyl sulfate (SDS) and peroxidase from horseradish (HRP) into a water-immiscible nematic LC and employed as a sensing platform for the detection of dichlorvos (2, 2-dichlorovinyl dimethyl phosphate, DDVP) that is a typical OP with acute toxicity. Remarkably, the stepwise release of the encapsulated cargo HRP from the W/LC emulsion can be triggered upon the addition of the cationic surfactant myristoylcholine chloride (Myr) due to the strong interfacial charge interactions with the anionic surfactant SDS. The released HRP induces an obvious color change of the overlaying bulk aqueous solution via the H2O2-HRP-TMB reaction system. As Myr can be enzymatically cleaved by AChE, the detection of AChE is fulfilled successfully. This approach is also employed to detect DDVP that can irreversibly inhibit the activity of AChE. This assay shows a linear response between the absorbance of the oxidized TMB solution and the DDVP concentration in the range of 0.001-10 μg/mL (R2 = 0.99). The limit of detection (LOD) and the limit of quantity (LOQ) of DDVP are determined to be 1.9 ng/mL and 6.3 ng/mL, respectively. In addition, this strategy also demonstrates excellent performance for the DDVP detection in real samples, the detection recovery rate of DDVP in water samples (lake water and tap water) and vegetables (tomatoes and cole) by this method is 88.0 % ∼112.6 %, the relative standard deviation (RSD) ≤ 7.5 %. These results suggest the W/LC emulsion-based sensing platform shows great potential for visual detection of DDVP in real samples. In conclusion, the proposed approach is scalable for practical application in food safety as well as environmental monitoring fields, and will provide promising solutions for the assay of pesticide residues.

Nanoplasmonic biosensors for multicolor visual analysis of acetylcholinesterase activity and drug inhibitor screening in point-of-care testing

The monitoring of acetylcholinesterase (AChE) activity and the screening of its inhibitors are significance of the diagnosis and drug therapy of nervous diseases. A metal ions-mediated signal amplification strategy was developed for the highly sensitive and multicolor assay of AChE activity and visually screening its drug inhibitors. After the specific reaction between AChE and acetylthiocholine (ATCh), the hydrolysis product thiocholine (TCh) can directly and decompose the α-FeOOH nanorods (NRs) to release amounts of Fe2+, which was regarded as Fenton reagent to efficiently catalyze H2O2 to produce ·OH. Then, the as-formed ·OH can further largely shorten the gold nanobipyramids (Au NBPs), generating a series of palpable color variations. The linear range for AChE activity was 0.01-500.0 U/L with the limit of detection as low as 0.0074 U/L. The vivid visual effects could be easily distinguished for the multicolor assay of AChE activity by naked eye in visible light. To achieve the point-of-care testing, Au NBPs were further assembled on polymeric electrospun nanofibrous films (ENFs) surface as test strips for the easy-to-use test of AChE activity by RGB values with a smartphone. Fascinatingly, this proposed strategy can be used for the visual screening AChE inhibitors or non-inhibitors. Comparing with the clinical drugs (rivastigmine tartrate, and donepezil), some natural alkaloids such as evodiamine, caffeine, camptothecin, and berberine hydrochloride were selected as inhibitor modes to confirm the drug screening capability of this method. This proposed strategy may have great potential in the other disease-related enzymatic biomarkers assay and the rapid screening of drug therapy.

Target-Driven Annular DNA Walker Coupled with Electrochemiluminescent Silicon Quantum Dots for APE1 Bioanalysis

Functional DNA walkers with substantial nanostructures have been extensively investigated; however, their stability still faces challenges when exposed to diverse nuclease in clinical biological samples, resulting in the unreliability of actual assessment. This work proposed a target-driven annular DNA walker with enhanced stability enabling the sensitive and reliable response to different concentrations of apurinic/apyrimidinic endonuclease 1 (APE1), by preparing silicon quantum dots (SiQDs) as electrochemiluminescence (ECL) emitters. Specifically, the SiQDs showed significant strong and stable ECL signals by purifying the microenvironment of SiQDs through the dialysis removal of the gel-like layers surrounding the SiQDs. The relative standard deviation (RSD) of their ECL signal had been improved 16.59 times under consecutive scanning compared to that of SiQDs without dialysis, demonstrating a significant improvement in ECL stability. Subsequently, in the presence of APE1, the designed annular DNA walker was activated to move along the numerous quenching probes within the continuous cross-based DNA orbits, which were immobilized to the SiQD-modified electrode, providing ECL readout signals. The linear range of this ECL biosensor was 1.0 × 10-13 U·μL-1 to 1.0 × 10-7 U·μL-1, and the limit of detection (LOD) was as low as 1.766 × 10-14 U·μL-1. This work provides a novel structure of a DNA walker with nuclease resistance for clinical sample detection and designs a new strategy for synthesizing SiQDs with favorable ECL performance, tremendously expanding the ECL application of SiQDs.

Sensitive detection of butyrylcholinesterase activity based on a stimuli-responsive fluorescence reaction

A fluorogenic reaction between the chelate of Mn(II)-citric acid and terephthalic acid (PTA) was discovered, which was carried out through heating the aqueous mixture of Mn²⁺, citric acid and PTA. Detailed investigations indicated the reaction products were 2-hydroxyterephthalic acid (PTA-OH), which was attributed to the reaction between PTA and OH, formed by the triggering of Mn(II)-citric acid in the presence of dissolved O₂. PTA-OH showed a strong blue fluorescence, peaked at 420 nm, and the fluorescence intensity presented a sensitive response to pH of the reaction system. Based on these mechanisms, the fluorogenic reaction was used for the detection of butyrylcholinesterase activity, achieving a detection limit of 0.15 U/L. The detection strategy was successfully applied in human serum samples, and it was also extended for the detection of organophosphorus pesticides and radical scavengers. Such a facile fluorogenic reaction and its stimuli-responsive properties offered an effective tool for designing detection pathways in the fields of clinical diagnosis, environmental monitoring and bioimaging.

Visual evaluation of acetylcholinesterase inhibition by an easy-to-operate assay based on N-doped carbon nanozyme with high stability and oxidase-like activity

Acetylcholinesterase (AChE) is the key enzyme associated with neurotransmission, and thus many drugs have been explored for their inhibitory effect on AChE, such as donepezil for Alzheimer's disease and organophosphorus pesticides (OPs). Compared with clinical trials, in vitro screening bioassays for AChE inhibitors are preferable in terms of operability and cost. Herein, we developed an easy-to-operate nanozyme-based colorimetric assay for the evaluation of AChE inhibitory strength with excellent anti-interference ability and low dependence on professional equipment. The metal-free carbon nanozyme NC900 played an important role in the signal output due to its features of efficient oxidase-like activity, excellent water dispersibility, high stability and low color interference. Employing various AChE-targeted or non-targeted pesticides as examples, the as-proposed assay exhibited excellent distinguishing ability for different chemicals. The higher absorption intensity at 652 nm represents a stronger inhibitory effect, as well as blue color. In addition, this method was used to study the influence of pH on the degradation of prodrugs, and the efficiency of mixed pesticides. This work provides a simple and reliable assay to screen AChE inhibitors, which is promising for the preliminary evaluation of a large number of potential candidates.

Chemical Mechanism-Dominated and Reporter-Tunable Surface-Enhanced Raman Scattering via Directional Supramolecular Assembly

Molecular resonance can be strengthened by charge transfer, profiting chemical mechanism (CM)-related surface-enhanced Raman scattering (SERS). Herein a supramolecular assembly enabled SERS system is established by functionalizing para-sulfonatocalix[4]arene (pSC₄) onto Au₃Cu nanocrystals (NCs). Due to the cooperation of Au and Cu, pSC₄ is directionally assembled on the surface of Au₃Cu NCs via van der Waals force, enabling photoinduced and hydrogen bond-induced charge transfer, which remarkably enhances the Raman scattering of methylene blue (MB) captured by pSC₄. In particular, for the C-N and C-C stretching of MB, the contributions of resonance Raman scattering increase up to 80%. In addition, the SERS system is able to display affinities of different host-guest interactions, and further employed to evaluate effects of drugs for Alzheimer's disease. In this work, charge transfer is realized by performing supramolecular assembly on the surface of plasmonic nanomaterials, providing an avenue to design CM-related and reporter-tunable SERS systems.

Synthesis of Copper Nanoclusters and Their Application for Environmental Pollutant Probes: A Review

Copper nanoclusters (CuNCs) as a new type of probe for environmental contaminants are gaining increasing attention because of its low cost, superior water dispersibility, wide availability and excellent optical properties. Compared with the other probes such as quantum dots and organic dyes, CuNCs show much more potential in practical application for their excellent photostability, large Stokes shift, low toxicity and other preponderance, especially in the fields of biosensing and environmental monitoring. Recently, the template-assisted synthesis of metal nanoclusters (MNCs) has been widely studied. A variety of templates such as proteins, small thiol molecules, polymers, and DNA with different spatial configuration have been used for the preparation of MNCs so far. This review primarily described recent advances in CuNCs in terms of the synthesis of CuNCs from different templates, the methods to improve the fluorescence (FL) properties of CuNCs, as well as the basic detection mechanisms based on the FL properties or catalytic properties. Finally, to promote the practical application of CuNCs probes, the challenges and prospects of CuNCs multifunctional probes are also discussed.