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Antioxidants are highly effective in preventing oxidative damage and reducing the risk of various diseases. To comprehensively evaluate the antioxidant content in food or nutrients, simple, portable, and cost-effective assays must be developed for measuring the total antioxidant capacity (TAC). In this study, gold nanobipyramids (AuNBPs) with a tunable photothermal effect were utilized as a probe to develop a straightforward method for photothermally sensing and assessing the TAC. Owing to the high refractive sensitivity of AuNBPs, antioxidant-triggered silver deposition induced drastic changes in their absorption spectra and photothermal effects. By this means, the TAC information can be converted into temperature signals easily captured using an affordable portable thermal camera. With our photothermal sensing strategy, the detection limit for ascorbic acid (a model antioxidant) is 0.08 μM, within the linear range of 0.1–100 μM. Furthermore, our method was successfully applied in practical applications for evaluating the TAC in honey and vitamin C tablets. The developed AuNBP-based photothermal assay exhibits considerable potential for portably assessing TAC. [ABSTRACT FROM AUTHOR]

The control of nanoparticle morphology can effectively change their properties. Adjusting the aggregation state of bovine serum albumin-coated gold nanoclusters (BSA-Au NCs) can regulate the enzyme-mimicking catalytic activity. Hyaluronic acid (HA) induces the aggregation of BSA-Au NCs, leading to the shielding of the catalytic active sites and a decrease in activity; this feature has been utilized to design a multicolor biosensor for hyaluronidase (HAase). The presence of HAase can hydrolyze the glycosidic bonds in HA, causing the aggregated BSA-Au NCs to disperse and express their catalytic activity, which in turn catalyzes the etching of Au nanobipyramids (Au-NBPs) in the presence of 3,3′,5,5′-tetramethylbenzidine (TMB), resulting in a morphological transition from bipyramidal to ellipsoidal and spherical shapes, while the solution displays a variety of colors. Visual recognition of these multicolor changes establishes a relationship between the enzyme activity and color. Based on the controlled aggregation and dispersion of BSA-Au NCs and the etching of Au-NBPs, a simple multicolor HAase biosensor was designed. The proposed biosensor shows a linear response to HAase concentrations in the range of 5–80 U/mL, with clear color changes under optimized conditions. The limit of detection (LOD) of the sensor was determined to be 1.98 U/mL (LOD = 3s/k). This method successfully applies the changing of enzyme-mimicking catalytic activity nanoparticles for colorimetric analysis detection. [ABSTRACT FROM AUTHOR]

The negative charge of nanoparticles affects their diffusion toward the negatively charged indium tin oxide (ITO) electrode, and this had been coupled with target-activated CRISPR/Cas12a to develop a homogeneous electrochemiluminescence (ECL) biosensor for human papillomavirus 16 (HPV 16) DNA (chosen as model target) detection. Tris-(2,2′-bipyridyl) ruthenium-(II) chloride hexahydrate-doped SiO2 nanoparticles (Ru@SiO2 NPs) with a diameter of about 50 nm was selected as the ECL probe.They were formed by encased Ru-(bpy)32+ in SiO2 nanoparticles, and this can effectively prevent the leakage of Ru-(bpy)32+ molecules and improve the stability of the probe. A hairpin probe (HP) was carefully designed and modified on the Ru@SiO2 NPs surface and resulted in the generation of a large negative charge on the surface of the nanoparticles. The strong electrostatic repulsion prevented the nanoparticles from reaching the negatively charged ITO electrode, leading to the weakness of the ECL signal detected. In the presence of a target, Cas12a is activated and the single-stranded region of HP is cleaved and separated from the Ru@SiO2 surface, resulting in less negative charge of the particles and enhanced ECL signal of the system. The ECL signal was linearly correlated with the logarithm of the HPV 16 DNA concentration in the range of 10 fM–10 nM with a limit of 3.4 fM (S/N = 3) under optimal conditions. The biosensor shows exceptional performance in the detection of HPV16 DNA in real samples. [ABSTRACT FROM AUTHOR]

The fluorescence (FL) activity of graphitic carbon nitride nanosheets (CNNSs) is dependent on both their band gap and surface defect states. It is known that the band gap of CNNSs is difficult to tune; however, studies on the regulation of the FL activity of CNNSs by surface defect states are still few. Herein a facile strategy to enhance the FL activity of CNNSs is developed by alkali-mediated passivation of the active defect states (dangling bonds) on CNNSs. With alkali treatment, the active defect states of CNNSs are eliminated and replaced with the passivated −NH2 groups, leading to significant enhancement of the FL quantum yields. We believe that this work will promote an understanding of the structure–FL properties of CNNSs, advancing an understanding of the luminous mechanisms and the application of CNNSs in FL sensing as well as biological imaging. [ABSTRACT FROM AUTHOR]

Column and row electrodes on two different glass substrates were orthogonally arranged in order to assemble an addressable microelectrode device for the purpose of comprehensive electrochemical detection. Amperometric signal at the individual crossing point of the column and row electrodes was detected separately on the basis of redox cycling of localized electroactive species occurring between the electrodes. The addressable microelectrode device was simple and could be easily assembled; however, it comprised as many as 10 x 10 addressable detection points on a single chip. The basic electrochemical performance of the device was investigated by using the ferricyanide/ferrocyanide redox couple. Electrochemieal responses at 100 individual points could be collected within 22 s. The present device was successfully used for imaging the spots of alkaline phosphatase on the array substrate. The results indicate that the device can be applied to comprehensive and high-throughput detection and imaging of biochemical species.

A new electrochemiluminescent (ECL) biosensor based on an electrically heated carbon paste electrode (HCPE) that was surface modified by xanthine oxidase (XOD) was designed and constructed in this work. It was found that the ECL intensity of luminol could be enhanced at the surface of XOD/HCPE by adding hypoxanthine (HX) to the solution, and there was a linear relationship between the ECL intensity and the concentration of HX. On the basis of this, an ECL enzyme biosensor can thus be developed to detect HX. However, because the activity of XOD is highly dependent on temperature, the biosensor is very sensitive to the temperature of the electrode. Also, because the temperature of the electrode may also affect the diffusion and convection of the luminescent compounds near the electrode surface, a suitable temperature for XOD/HCPE has to be controlled to achieve the best ECL signal. The key feature of the designed biosensor is that the temperature of the electrode is controllable so the most suitable temperature for the enzyme reaction can be obtained. The obtained results showed that the ECL enzyme biosensor exhibited the best sensitivity at an electrode temperature of 35[degrees]C for the detection of HX. The detection limit was 30-fold lower than that at room temperature (25[degrees]C).

The application of surface-enhanced Raman scattering (SERS) in aqueous sample detection is normally limited by the low affinity between analytes and SERS-active nanoparticles. Furthermore, a tendency of uncontrollable aggregation of solute (nanoparticles or analytes) can cause poor reproducibility of the detected SERS signal. Herein, a ready-to-use plasmonic gel bead was developed for rapid and effective detection of aqueous samples with high sensitivity and reproducibility. The SERS gel bead is made of calcium alginate gel beads (CAGBs) that contain gold nanobipyramids (Au NBPs) and an aqueous sample, which can be prepared and detected within only 1 min. Au NBPs/CAGBs can generate an in-depth three-dimensional SERS-active gel network for trapping analytes and offering a uniform hotspot region, which produces a reproducible and uniform signal. Using rhodamine 6G as a model target, the proposed method exhibits excellent reproducibility with a relative standard deviation of 6.57% and a detection limit of 0.4 nM. Then, Au NBPs/CAGBs were applied to quantitatively detect serum uric acid in the range of 10–1000 μM and a limit of detection of 0.18 μM, and the results were strongly consistent with those of the commercial ELISA method. This work offers a low-cost and easy route for the fabrication of a versatile SERS substrate for monitoring disease-related biomarkers and point-of-care testing. [ABSTRACT FROM AUTHOR]

Electrochemiluminescence (ECL) sensors have been widely developed because of their high sensitivity and low background. However, most of them suffered from tedious probe modification on the electrode and cross-interferences within the sensing and reporting reactions. The bipolar electrode based ECL (BPE-ECL) can effectively eliminate interference by physically separating the sensing and reporting cells, but there is still a need for exogenous electroactive indicators to transduce the variations between two poles of a BPE. Herein, based on the discovery that conductivity can be regulated in aqueous medium by homogeneous bioreaction, we showed a novel BPE-ECL sensing platform that combined the conductivity-based biosensing technology with ECL reporting system for the first time. Compared to many short nucleic acids, the target induced a hybridization chain reaction to produce the long nucleic acid aggregates, resulting in a conductivity decrease of the sensing cell and finally reducing the ECL response in the reporting cell. The BPE-ECL platform has already been applied to detect microRNA-21 for a demonstration. This innovative system not only separates the target sensing and reporting reactions but also avoids the use of electrochemical indicators for measurement. The BPE-ECL biosensing platform can be developed to detect different targets by changing the probe used.

Halide perovskites have emerged as a highly promising class of photoelectric materials. However, the application of lead-based perovskites has been hindered by their toxicity and relatively weak stability. In this work, a composite material comprising a lead-free perovskite cesium copper iodide (CsCu 2 I 3 ) nanocrystal and a metal-organic framework (MOF-801) has been synthesized through an in situ growth approach. The resulting composite material, denoted as CsCu 2 I 3 /MOF-801, demonstrates outstanding stability and exceptional optoelectronic characteristics. MOF-801 may serve a dual role by acting as a protective barrier between CsCu 2 I 3 nanocrystals and the external environment, as well as promoting the efficient transfer of photogenerated charge carriers, thereby mitigating their recombination. Consequently, CsCu 2 I 3 /MOF-801 demonstrates its utility by providing both stability and a notably high initial photocurrent. Leveraging the inherent reactivity between H 2 S and the composite material, which results in the formation of Cu 2 S and structural alteration, an exceptionally sensitive photoelectrochemical sensor for H 2 S detection has been designed. This sensor exhibits a linear detection range spanning from 0.005 to 100 μM with a remarkable detection limit of 1.67 nM, rendering it highly suitable for precise quantification of H 2 S in rat brains. This eco-friendly sensor significantly broadens the application horizon of perovskite materials and lays a robust foundation for their future commercialization.

Bisphenol compounds (BPs) have recently been the subject of growing interest due to their wide use in industrial and consumer products. Besides their adverse effects on human endocrine system, effective extraction of BPs and their elimination from complex sample matrix are still significant challenges in food analysis. Herein, a novel Zr(IV)-based metal-organic framework (MOF), named BUT-16, has been synthesized and utilized for the extraction and enrichment of BPs in milk samples. Bisphenol A (BPA), one of the highest production volume BPs, is used as a model molecule. The uptake capacity for BPA can reach up to 48 mg/g, and the adsorption rate is rapid (∼10 min), because of the larger surface area and cooperation of multiple functionalities of BUT-16. Employing BUT-16 in solid-phase extraction, coupled with ultra-performance liquid chromatography-tandem mass spectrometry detection, we generated a rapid, facile, and robust method for the enrichment and detection of trace BPA and its 12 substitutes in milk samples. After optimization, the limits of detection and quantification for BPs can be achieved as low as 0.05 and 0.2 ng/mL, respectively. Without the correction of the isotopic internal standard, the average recoveries of BPs at the different spiked concentrations varied from 63.8 to 120.6%, with a satisfactory precision (RSD ≤ 8.2%). Furthermore, the proposed method was successfully applied to the detection of BPs in real milk samples, and the results were in accordance with those of methods reported previously.