Antimony selenide/graphene oxide composite for sensitive photoelectrochemical detection of DNA methyltransferase activity.

Antimony selenide (Sb2Se3) as a p-type semiconductor material has recently attracted extensive attention for its excellent photoelectric properties in applications of thin film solar cells. However, applying Sb2Se3 as a photoelectrochemically (PEC) active material for constructing biosensors has never been reported. In this work, by using Sb2Se3/graphene oxide (Sb2Se3-GO) as both the PEC probe and substrate for biomolecule conjugation, a "signal-off" sandwich-type PEC biosensor was proposed for DNA methyltransferase (Dam MTase) activity detection based on gold nanoparticles (Au NPs) as quenchers. In the presence of Dam MTase and Dpn I, hairpin probe DNA (hDNA) was cleaved into single-stranded DNA (ssDNA), which could be hybridized with Au NP-functionalized DNA (S1) to form a double-stranded DNA (dsDNA) complex. The formation of dsDNA shortened the distance between Au NPs and Sb2Se3 on the electrode and induced competitive absorption and exciton energy transfer (EET) between Sb2Se3 and the Au NPs, thus significantly reducing the photocurrent. The constructed PEC biosensor exhibited a superior performance compared to most reports with a wide detection range from 1 mU mL-1 to 100 U mL-1 and a low detection limit of 0.6 mU mL-1 for the detection of Dam MTase. This work opens a new avenue for Sb2Se3 in biosensing applications and provides a new technology for the early warning and early diagnosis of diseases.

Engineering of CdTe/SiO2 nanocomposites: Enhanced signal amplification and biocompatibility for electrochemiluminescent immunoassay of alpha-fetoprotein.

Electrochemiluminescent (ECL) performance and cytotoxicity of CdTe quantum dots (QDs)-based nanocomposites and its possible application for ECL immunoassay were investigated. Two types of CdTe-based nanocomposites, i.e., SiO2-coated CdTe (CdTe@SiO2) and CdTe-functionalized SiO2 (SiO2@CdTe), were synthesized and comprehensively compared in regarding of the cytotoxicity and ECL performance. The in vitro cytotoxicity of SiO2@CdTe and CdTe@SiO2 nanoparticles was assessed in L02 cells using standard CCK-8 assay, and their ECL performance was investigated by constructing sandwiched immunosensor using SiO2@CdTe and CdTe@SiO2 as tags for the labelled antibody, respectively. The results showed that CdTe@SiO2 exhibited much lower cytotoxicity and a higher ECL intensity than SiO2@CdTe. Taking the analysis of alpha-fetoprotein (AFP) as an example, the ECL immunosensor using CdTe@SiO2 as an emitter was proved to have a wide linear dynamic range from 1.0 pg mL-1 to 100 ng mL-1 with a low detection limit of 0.22 pg mL-1 (S/N ratio of 3). The ECL immunosensor also demonstrated satisfactory recovery and excellent reproducibility and stability, indicating that this method has prospects in practical application in the clinical diagnosis of AFP.

Metal-Free All-Carbon Nanohybrid for Ultrasensitive Photoelectrochemical Immunosensing of alpha-Fetoprotein.

C60 can accept up to six electrons reversibly and show exceptional light absorption over the entire UV-vis spectrum, making it a potential photoactive probe for photoelectrochemical (PEC) bioassay. However, few successful works have been reported to apply fullerenes in PEC biosensing, partially because of the low electronic conductivity and poor interfacial interactions with targeted biomolecules. Herein, we report the addressing of these two obstacles by coupling high conductive graphite flake (Gr), graphene oxide (GO) with sufficient oxygen-containing functional groups, and an alkylated C60 (AC60) into a metal-free all-carbon nanohybrid (AC60-Gr-GO) via harnessing delicate noncovalent interactions among them through a facile mechanical grinding. It was revealed that the as-obtained AC60-Gr-GO nanohybrid not only showed conspicuous enhancement of photocurrent up to 35 times but also offered rich anchors for bioconjugation. With detection of alpha-fetoprotein as an example, the AC60-Gr-GO based PEC immunosensor demonstrated a broad linear detection range (1 pg·mL-1 to 100 ng·mL-1) and a detection limit as low as 0.54 pg·mL-1, superior/competitive to PEC immunosensors for AFP in previous reports. By a proper reinforcement in conductivity and biointerface engineering, this work may provide a new way to use fullerenes as photoactive materials in more general PEC biosensing.

Direct Immunoassay for Facile and Sensitive Detection of Small Molecule Aflatoxin B1 based on Nanobody.

Aflatoxin B1 (AFB1 ), one of the most toxic mycotoxins, is classified as a group I carcinogen and ubiquitous in various foods and agriproducts. Thus, accurate and sensitive determination of AFB1 is of great significance to meet the criteria of food safety. Direct detection of AFB1 is difficult by monoclonal antibody (mAb) with large molecular size (≈150 kD) since the target is too small to produce a detectable signal change. Herein, by combining the electrochemical properties of nanomaterials and the advantages of nanobodies, we developed a direct, highly selective and sensitive electrochemical immunosensor for small molecule detection. The proposed immunosensor had a wide calibration range of 0.01 to 100 ng mL-1 and a low detection limit of 3.3 pg mL-1 (S/N=3). Compared with the immunosensor prepared with mAb which was applied in the typical indirect immunoassay, the immunosensor in this work possessed two orders of magnitudes wider linear range and 10-fold more sensitivity. The as-obtained immunosensor was further successfully applied for sensing AFB1 in real samples. This proposed assay would provide a simple, highly sensitive and selective approach for the direct immunoassay of small molecule AFB1 , and is extendable to the development of direct immunosensing systems for other small molecules detection by coupling nanocarbon and nanobody.