Isolation of aptamers with excellent cross-reactivity and specificity to sulfonamides towards a ratiometric fluorescent aptasensor for the detection of nine sulfonamides in seafood.

Sulfonamides (SAs) is a class of antibiotics that extensively used for treating infectious diseases in livestock industries and aquaculture. Thus, it is urgent need to obtain the bio-receptor, which has excellent cross-reactivity and specificity to SAs, for developing high-throughput methods for the determination of multiple SAs even all commonly-used SAs, to realize the quick screening/detection of total SAs in animal-derived foods. We herein isolated several SAs-specific cross-reactive aptamers by using a library-immobilized SELEX with multi-SAs parallel selection strategy. Two of the isolated aptamers (Sul-01 and Sul-04) can specifically recognize and bind seven SAs respectively with higher binding affinity and no interference of non-sulfonamide antibiotics, and thus can be applied as bio-receptors for developing high-throughput aptasensors for the quick screening/detection of multiple SAs. By using the mixture of Sul-01 and Sul-04 as bio-receptor, a ratiometric fluorescent aptasensor was created for the quick detection of nine SAs including sulfamethoxydiazine (SMD), sulfapyridine (SPD), sulfaquinoxaline (SQ), sulfathiazole (ST), sulfamonomethoxine (SMM), sulfamerazine (SMR), sulfaguanidine (SG), sulfamethazine (SMZ) and sulfadiazine (SD) with a detection limit (LOD) of 0.10-0.50 µM, or total of above nine SAs with a LOD of 0.20 µM. The fluorescent aptasensor was successfully applied to detect each or total of SMD, SPD, SQ, ST, SMM, SMR, SG, SMZ and SD in fish samples with a recovery of 83 %-92 % and a relative standard deviation (RSD, n = 5) < 5 %. This study not only provided several promising bio-receptors for the development of diverse high-throughput aptasensors to achieve the quick screening of multiple SAs residues, but also provided a simple, stable and sensitive method for the quick screening of SMD, SPD, SQ, ST, SMM, SMR, SG, SMZ and SD in seafood.

Sensitive detection and intracellular imaging of free copper ions based on DNA-templated silver nanoclusters aggregation-inducing fluorescence enhancement effect.

Free copper ions (Cu+ and Cu2+) have critical toxicity to cells, although copper is an essential element for human body. Hence, sensitive monitoring is crucial to avoid over intake of Cu+/Cu2+. We herein designed a ssDNA sequence (A31) for synthetizing A31-templated silver nanoclusters (AgNCs), and demonstrated that Cu+/Cu2+ can induce the aggregation of A31-templated AgNCs and thus greatly enhanced the fluorescence emission of A31-templated AgNCs. Based on Cu+/Cu2+-induced fluorescence enhancement effect of A31-templated AgNCs, a label-free and signal-on fluorescent sensing platform was developed for the specific and sensitive detection of Cu+/Cu2+ in biological samples and intracellular imaging of Cu+/Cu2+ in cells. The signal-on fluorescent sensing platform could be used to rapidly detect Cu+ and Cu2+ with a detection limit of 0.1 µM within 30 min., and to perform the intracellular imaging of Cu+ and Cu2+ in cells with good cell permeability and biocompatibility. By using the signal-on fluorescent sensing platform, we have successfully detected Cu+ and Cu2+ in cells fluids and human serum with a recovery of 90-104% and a RSD (n = 5) < 5%, and performed the imaging of Cu+/Cu2+ in Hela cells. The developed fluorescent sensing platform has obvious analytical and imaging advantages such as signal-on, simple operation, short analysis time, both Cu+ and Cu2+ detection, similar or higher sensitivity, good cell permeability and biocompatibility, which promising a reliable approach for the rapid and on-site detection or imaging of free copper ions in biological samples in clinical diagnosis.

In vitro bio-accessibility and distribution characteristic of each arsenic species in different fishes and shellfishes/shrimps collected from Fujian of China.

It is very important to consider the bio-accessibilities and concentrations of each arsenic species, not total arsenic, in seafood in order to accurately assess internal exposure level and health risk of arsenic from seafood. Herein, the concentrations and in vitro bio-accessibilities of each arsenic species in various fishes and shellfishes/shrimps were extensively investigated. Experimental results showed that arsenic species and contents in shellfishes/fishes remarkably varied with the difference of fish/shellfish species or individuals and sampling area, and arsenobetaine (AsB) is dominant arsenic species for fishes and shellfishes/shrimps. Different arsenic species in the same fish/shellfish have quite different bio-accessibilities, and the bio-accessibilities of each arsenic species also varied with fish/shellfish species or individuals. As3+ in fishes/shellfishes was partly oxidized to form As5+ during gastrointestinal digestion, and thus it is more reasonable and practicable to evaluate the bio-accessibilities of inorganic arsenic (iAs, total As3+ and As5+), not individual As3+ and As5+. Fishes and shellfishes/shrimps have similar bio-accessibilities of iAs, AsB and total arsenic, whereas have different bio-accessibilities of MMA (monomethylarsonic acid), DMA (dimethylarsinic acid), and two un-identified arsenic (Ui-As1 and Ui-As2). The results of this study provided a valuable knowledge for accurately assessing the health risk of arsenic in seafood.