Visible-light driven label-free photoelectrochemical immunosensor based on TiO2/S-BiVO4@Ag2S nanocomposites for sensitive detection OTA

Ultrasensitive label- and amplification-free photoelectric protocols based on sandwiched layer-by-layer plasmonic nanocomposite films for the detection of alpha-fetoprotein

A label- and amplification-free photoelectric immunosensor based on well-defined layer-by-layer sandwich-structured AuNP/TNW/AuNP composite is proposed for direct and ultrasensitive detection of α-fetoprotein (AFP). The AuNP/TNW/AuNP composite is produced by assembling an Au nanoparticle underlayer and anatase TiO₂ nanowires (TNW) onto the FTO substrate, followed by decorating Au nanoparticles onto the TNW surface, through a simple sputtering and hydrothermal process. The resulting AuNP/TNW/AuNP electrode exhibits a 14-fold and 2-fold enhancement in photocurrent density under simulated sunlight compared with that of bare TNW and AuNP/TNW, respectively, which benefits from the SPR-induced photoabsorption increment and charge separation improvement in Au nanoparticle and interfacial charge transfer promotion at the TiO₂/substrate interface in the Au underlayer. As a proof of concept, the AFP antigen can be quantitatively detected by the proposed AuNP/TNW/AuNP coupled with anti-AFP through the analysis of the photocurrent change. This novel AFP photoelectric immunosensor exhibited sensitive detection of AFP with an ultrahigh sensitivity of 0.001 ng mL^-1 and good specific selectivity. Moreover, the practical determination of AFP in human serum is also investigated, demonstrating its applicability and potential attraction for clinical tests and disease diagnosis.

Sensitive aptamer-based fluorescene assay for ochratoxin A based on RNase H signal amplification

A new assay for the selective and sensitive aptamer-based fluorescent biosensor for ochratoxin A (OTA) detection is proposed. It consists of a ribonuclease H (RNase H)-assisted cycle response that leads to a significant amplification of the signal, which allow for a low limit of detection (LOD) of 0.08 ng/mL. By using this technique, a high selectivity for OTA against ochratoxin B and aflatoxin B₁ (AFB₁) was noticed. The quantitative determination in real samples has been verified using red wine samples spiked with a series of OTA concentrations (0.4, 4, and 12 ng/mL), and the recoveries ranged from 96.1 to 107.5%. This aptasensor has great practical applications in food industry and moreover, can be extended for the detection of other toxins by replacing the sequence of the recognition aptamer.

Red light-driven photoelectrochemical biosensing for ultrasensitive and scatheless assay of tumor cells based on hypotoxic AgInS2 nanoparticles

A novel red light-driven photoelectrochemical (PEC) biosensing platform based on hypotoxic ternary mercaptopropionic acid (MPA)-capped AgInS₂ nanoparticles (NPs) with excellent hydrophily and biocompatibility was proposed. AgInS₂ NPs as a PEC sensing substrate exhibited high photon-to-current conversion efficiency under red light excitation, generating an intensive photocurrent for enhancing the sensitivity of PEC determination. After the introduction of the amino-terminated sgc8c aptamer onto the interface of AgInS₂ NPs, the overexpressed protein tyrosine kinase-7 on the surface of lymphoblast CCRF-CEM cells could be efficiently captured. Using CCRF-CEM cell as a model analyte, an ultrasensitive PEC biosensor for scatheless assay of cells at the applied potential of 0.15 V under a red light excitation of 630 nm was designed based on the significant decline of photocurrent intensity after capturing CCRF-CEM cells. The developed PEC cytosensor demonstrated an excellent cell-capture ability, as well as a wide linear range from 1.5 × 10² to 3.0 × 10⁵ cells/mL and a low detection limit of 16 cells/mL for CCRF-CEM cells. In addition, the resulting assay method verified high selectivity and negligible cytotoxicity for cells assay. This work provided an alternative method for scatheless assay of tumor cells, which would have promising prospect in clinical diagnoses of cancer.

Treatment of wastewater containing Reactive Brilliant Blue KN-R using TiO2/BC composite as heterogeneous photocatalyst and adsorbent

Heterogeneous photocatalysis namely titanium dioxide (TiO₂) supported on coconut shell biochar (BC) was synthesized by sol-gel method (calcined at 450 °C) in the paper, which was innovatively applied to the decolorization of Reactive Brilliant Blue KN-R. The transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD) results demonstrated that anatase TiO₂ film was firmly immobilized on the surface and pores of BC. The photocatalysis tests under UV high pressure xenon lamp (300 W) showed highest decolorization efficiency occurred at strong acid and alkali conditions (pH = 1 and 11) reached as 99.71% and 96.99% respectively within 60 min. Therefore, the TiO₂/BC composites demonstrated both photocatalytic and adsorption capacity on KN-R decolorized, and presented quite durable and reusable in regeneration cycles, indicating a widely application possibility in anthraquinones dyeing wastewater treatment.

A fluorometric aptamer-based assay for ochratoxin A using magnetic separation and a cationic conjugated fluorescent polymer

A fluorometric aptamer-based assay for ochratoxin A (OTA) is described. It is making use of magnetic separation and a cationic conjugated fluorescent polymer. Amino-tagged aptamer (Apt) against OTA is immobilized on magnetic beads (MBs) to form a conjugate of type Apt-MBs. The immobilized aptamer is partially complementary to carboxyfluorescein-labeled DNA which binds to the Apt-MBs via hybridization if OTA is absent. Only few FAM-DNA will remain in the supernatant after magnetic separation, and only weak fluorescence resonance energy transfer (FRET) occurs on addition of the fluorescent polymer. If, however, OTA is present, it will bind to the aptamer and prevent the hybridization between Apt-DNA and FAM-DNA. This results in the presence of large amounts of FAM-DNA in the supernatant after magnetic separation. On addition of fluorescent polymer, efficient FRET occurs from the polymer to FAM-DNA. Fluorescence, best measured at excitation/emission peaks of 370/530 nm, increases with increasing concentrations of OTA. This assay is highly sensitive and selective. The detection limit is as low as 0.11 ng mL^-1. This is 6 times lower than the aptamer assay without using the fluorescent polymer. Conceivably, this method has a wider scope in that it may be extended to other mycotoxins by simply changing the aptamer. Graphical Abstract Schematic of a fluorometric aptamer assay for ochratoxin A (OTA). It is based on magnetic separation coupled with a cationic conjugated polymer (PFP).

Label-Free G-Quadruplex Aptamer Fluorescence Assay for Ochratoxin A Using a Thioflavin T Probe

Ochratoxin A (OTA) is one of the most common mycotoxins contaminating feed and foodstuffs. Therefore, a great deal of concern is associated with AFB1 toxicity. In this work, a fast and sensitive fluorescence aptamer biosensor has been proposed for the OTA assay. In the absence of OTA, the OTA aptamer can form a G-quadruplex structure with thioflavin T (ThT) dye, which results in increased fluorescence. After joining OTA, OTA aptamer combines with OTA and the G-quadruplex can be formed. Only faint fluorescence was finally observed when ThT weakly reacts with the quadruplex. Through this test method, the entire reaction and analysis process of OTA can be completed in 10 min. Under optimal experimental conditions (600 nM OTA-APT, 7 μM ThT, and 3 min incubation time), this proposed assay has a good limit of detection (LOD) of 0.4 ng/mL and shows a good linear relationship within the range of 1.2⁻200 ng/mL under the best experimental conditions. This method has a high specificity for OTA relative to Ochratoxin B (23%) and Aflatoxin B₁ (13%). In addition, the quantitative determination of this method in real samples has been validated using a sample of red wine supplemented with a range of OTA concentrations (1.2 ng/mL, 12 ng/mL, and 40 ng/mL) with recoveries of 96.5% to 107%.

A novel sandwich-type photoelectrochemical sensor for SCCA detection based on Ag2S-sensitized BiOI matrix and AucorePdshell nanoflower label for signal amplification

Signal amplification was fulfilled for the interaction between BiOI/Ag₂S and Au_cPd_s.

Inner filter with carbon quantum dots: A selective sensing platform for detection of hematin in human red cells

Hematin plays a crucial role in various physiological functions, and the determination of hematin in complex biological matrixes is a significant but difficult issue. Considering the unique photophysical/photochemical properties of carbon quantum dots (CQDs) prepared with p-aminobenzoic acid (PABA) and ethanol, a new strategy for the design of fluorescent probes for hematin has been achieved. The proposed sensor array is fabricated based on the inner filter effect (IFE) between hematin and CQDs with phenomenon of selective fluorescence quenching of CQDs which results from the strong absorption of the excitation and emission spectrum of CQDs by hematin. The fluorescence quenching of CQDs is closely related to the amount of hematin and there is a good linear relationship over the range of 0.5-10μM with a detection limit of 0.25μM. What's more, the fluorescence assay has been successfully applied for hematin sensing in healthy human red cells showing this sensing assay has a great potential prospect for detection of hematin in the complex matrixes.