A low-field nuclear magnetic resonance DNA-hydrogel nanoprobe for bisphenol A determination in drinking water.

A low-field nuclear magnetic resonance (LF-NMR) DNA-hydrogel (LNDH) nanoprobe was designed for bisphenol A (BPA) determination. It consists of Fe3O4 superparamagnetic iron oxide nanoparticles (SPIONs) and a DNA-hydrogel technology. Fe3O4 SPIONs were encapsulated in the DNA-hydrogel to form an aggregated state. After adding BPA, the gel system transformed into a sol gel due to the target-aptamer specific binding. The coated gathered particles dispersed and thus, the relaxation time T2 declined. The LNDH nanoprobe was developed to realize a simple, sensitive, and effective BPA determination method without repeated magnetic separation steps. Under the optimal experimental conditions, the determination range of the LNDH biosensor was 10-2~102 ng mL-1 and the limit of determination was 0.07 ng mL-1. The LNDH nanoprobe was applied to two kinds of water samples (tap water and bottled water). The recovery ranged from 87.85 to approximately 97.87%. This strategy offered a new method to detect BPA by LF-NMR. It is also expected to be applicable in related fields of food safety determination, environmental monitoring, and clinical diagnosis. Graphical abstract Schematic presentation of LNDH biosensor. Acrydite-modified ssDNA was copolymerized with acrylamide to form linear conjugates PS-A/B, adding aptamer and SPIONs to form DNA-hydrogel. When aptamer captured the target, the hydrogel was destroyed to disperse the coated SPIONs. T2 relaxation time declined.

Turn-on fluorometric immunosensor for diethylstilbestrol based on the use of air-stable polydopamine-functionalized black phosphorus and upconversion nanoparticles.

The preparation of air-stable black phosphorus (BP) is challenging because atomic layers of BP degrade rapidly on exposure to oxygen. A strategy is presented for the synthesis of BP functionalized with polydopamine (PDA/BP). Dopamine was self-polymerized to yield polydopamine (PDA) which then was used to coat the surface of BP. PDA can be easily reduced and this prevents BP degradation. PDA/BP also is a viable matrix for the adsorption of proteins due to the presence of functional groups. Without any chemical activation, diethylstilbestrol (DES)-specific monoclonal antibody was adsorbed on the PDA/BP surface. PDA/BP quenches the fluorescence antigen-modified NaYF4:Yb,Ho,Nd upconversion nanoparticles (UCNPs; photoexcited at 808 nm) via specific immuno recognition. Exposure to DES causes the dissociation of UCNP from the PDA/BP surface and fluorescence at 475, 525, 545 and 660 nm to recover. This is due to the DES competition with antigen for binding to the antibody. Based on this competitive immuno mechanism, a turn-on fluorometric immunoassay was constructed. It has a response that covers the 0.1 to 1000 ng mL-1 DES concentration range with a detection limit of 83 pg mL-1. This method was successfully applied to the determination of DES in spiked food and human urine samples. Graphical abstract Air-stable polydopamine-functionalized black phosphorus was obtained by modification of black phosphorus with polydopamine and then was coupled with specific monoclonal antibody. Combined with antigen-modified upconversion nanoparticles, a turn-on fluorometric immunoassay was constructed to detect diethylstilbestrol.

Low field nuclear magnetic sensing technology based on hydrogel-coated superparamagnetic particles.

Based on superparamagnetic nanoparticles, a responsive polyacrylamide hydrogel self-assembled by nucleic acid hairpin hybridization chain reaction was designed, and a universal low field nuclear magnetic resonance sensing platform was successfully constructed. As the target was gradually added, the hydrogel coating on the surface of the magnetic nanoparticle was opened layer by layer through binding with the aptamer, which specifically bonded thereto, causing different degrees of exposure of the magnetic nanoparticle, resulting in changes of low field nuclear magnetic resonance signals. This method was originally applied to the rapid detection of adenosine triphosphate (ATP), and the versatility of the method was verified using polychlorinated biphenyl 77 (PCB77). This method had the advantage of being fast, convenient, and low cost, and it can be easily operated with high repeatability. This universal method can detect a variety of targets by replacing aptamers and may be useful in controlling food quality and for rapidly detecting cancer cells in vitro.