Allosteric switch for electrochemical aptasensor toward heavy metals pollution of Lentinus edodes sensitized with porphyrinic metal-organic frameworks.

BACKGROUND: Lentinan medicament from Lentinus edodes has been considered as natural medicinal products with minimal side effects for cancer therapy, but Lentinus edodes are easily polluted by nonbiodegradable heavy metals, especially silver ion (Ag+). Therefore, it is highly desirable to monitor Ag + pollution in Lentinus edodes considering their adverse impact on lentinan medicament. Electrochemical sensor isn't affected from the interference of matrix turbidity and color, and offers a powerful means for determination of variant analytes. As for electrochemical sensing toward Ag+, there is a great need to design efficient signal probes for specific recognition and signal generation. RESULTS: We present an appropriate electrochemical aptasensor for Ag + assay based on biomimetic catalysis of porphyrin-encapsulated MOF (PorMOF) and allosteric switch of C-rich DNA. Thanks to the excellent biocompatibility, PorMOFs as nanozyme are used to design signal probes by loading duplex-like DNA scaffold. Owing to the specific recognition of Ag+ toward cytosine (C) base-rich DNA, PorMOF at the distal end was close to the underlying electrode via C-Ag+-C formation, leading to an enhanced current of catalytic hydroxylamine oxidation for signal generation. Using the positive correlation between current response and Ag+ level, the electrochemical system provides a promising means for on-line monitoring of Ag+ in Lentinus edodes with recoveries from 92.8% to 106.4% and relative standard deviation from 3.98% to 8.24%, verifying the applicability of the electrochemical aptasensor toward Ag+ in Lentinus edodes. SIGNIFICANCE AND NOVELTY: With merits of portability, simple operation, and rapid response, the electrochemical pattern offers a useful solution for on-line monitoring of Ag+ in Lentinus edodes. By altering the DNA sequence, the proposed aptasensor provides a powerful way for monitoring other heavy metals, capable of protecting medicament production from heavy metal pollution.

Structure-Switching Electrochemical Aptasensor for Single-Step and Specific Detection of Trace Mercury in Dairy Products.

A reagentless and single-step electrochemical aptasensor with separation-free fashion and rapid response is developed for the Hg2+ assay in dairy products. Herein, the sensing strategy is established on Hg2+-induced structural transition of the methylene-blue-tagged single-stranded DNA (ssDNA) from a flexible manner to rigid hairpin-shaped double-stranded DNA (dsDNA), generating an improved peak current for the Hg2+ assay with a detection limit of 0.62 fM. Importantly, the best signal-to-noise ratio value can be obtained by exploiting Au flowers as sensing material and the optimal ssDNA concentration. The proposed sensor also exhibits high selectivity as a result of the specific thymine-Hg2+-thymine (T-Hg2+-T) coordination chemistry and can be applied to detect Hg2+ in dairy products. With the use of the electric "signal-on" switch, the electrochemical aptasensor has the advantages of simplicity, ease of operation, and high sensitivity and specificity, offering a promising method to assess the safety of dairy products polluted with Hg2+.

Functionalized nanocomposites with the optimal graphene oxide/Au ratio for amplified immunoassay of E. coli to estimate quality deterioration in dairy product.

An amplified electrochemical immunosensor was developed by exploiting poly(diallyldimethylammonium chloride)-functionalized graphene oxide and gold nanoparticles (GO-PDDA@AuNP) as sensing platform. Highlight of this work was to investigate and optimize the ratio of GO-PDDA to AuNP for sensitivity enhancement. The suitable GO-PDDA@AuNP nanocomposites were proven to not only provide an excellent biocompatible microenvironment for the immobilized antibody, but also accelerate electron transfer to enhance electrochemical signal. Moreover, the {dAb-Au-THi} nanoprobes as biorecognition elements were designed by utilizing the amplification effect of AuNPs to load detection antibody (dAb) and enormous thionine (THi), in which dAb was used for specific recognition of E. coli and THi served as electroactive species. Under optimal conditions, experimental results demonstrated that the variations (ΔI) in the peak current linearly depended on the logarithmic value of E. coli concentration from 50 to 5.0×106cfumL-1 with the detection limit of 35cfumL-1. Recovery experiments were also performed for E. coli assay in dairy product (pure fresh milk, yogurt in shelf-life and expired yogurt), and the recoveries of standard additions were in the range of 89.7-112.6%. The excellent performance of the proposed strategy indicated its promising prospect as a valuable tool to estimate the quality deterioration in dairy product.

Optimized dendrimer-encapsulated gold nanoparticles and enhanced carbon nanotube nanoprobes for amplified electrochemical immunoassay of E. coli in dairy product based on enzymatically induced deposition of polyaniline.

A highly sensitive immunosensor was reported for Escherichia coli assay in dairy product based on electrochemical measurement of polyaniline (PAn) that was catalytically deposited by horseradish peroxidase (HRP) labels. Herein, the immunosensor was developed by using poly(amidoamine) dendrimer-encapsulated gold nanoparticles (PAMAM(Au)) as sensing platform. Importantly, the optimal HAuCl4/PAMAM ratio was investigated to design the efficient PAMAM(Au) nanocomposites. The nanocomposites were proven to not only increase the amount of immobilized capture antibody (cAb), but also accelerate the electron transfer process. Moreover, the {dAb-CNT-HRP} nanoprobes were prepared by exploiting the amplification effect of multiwalled carbon nanotubes (CNTs) for loading detection antibody (dAb) and enormous HRP labels. After a sandwich immunoreaction, the quantitatively captured nanoprobes could catalyze oxidation aniline to produce electroactive PAn for electrochemical measurement. On the basis of signal amplification of the PAMAM(Au)-based immunosensor and the {dAb-CNT-HRP} nanoprobes, the proposed strategy exhibited a linear relationship between the peak current of PAn and the logarithmic value of E. coli concentration ranging from 1.0 × 10(2) to 1.0 × 10(6) cfu mL(-1) with a detection limit of 50 cfu mL(-1) (S/N=3), and the electrochemical detection of E. coli could be achieved in 3h. The electrochemical immunosensor was also used to determine E. coli in dairy product (pure fresh milk, infant milk powder, yogurt in shelf-life and expired yogurt), and the recoveries of standard additions were in the range of 96.8-108.7%. Overall, this method gave a useful protocol for E. coli assay with high sensitivity, acceptable accuracy and satisfying stability, and thus provided a powerful tool to estimate the quality of dairy product.