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In this work, a novel reversed phase/cation exchange mixed-mode sorbent for solid phase extraction (SPE) was synthesized by modifying the mesoporous material MCM-41 with 3-aminopropyltriethoxysilane (APTES) and octadecyltrimethoxysilane (C18 TMS) followed by succinic acid glycoside (SAA) in two steps. Various SPE parameters were optimized, and an analytical method was developed for the determination of six aminoglycosides (AGs) in milk by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) using an amide column for chromatographic separation. The results of structural characterization demonstrated that the synthesized material had a large specific surface area, uniform pore size, and modified functional groups, exhibiting strong adsorption capacity and selectivity for AGs. The bifunctionalized material significantly improved matrix interference of milk compared to the carboxylated material. The proposed method exhibited good linearity for the six AGs in the concentration range of 5–500 ng/mL with correlation coefficients of 0.992 7–0.999 5. The limits of detection (LOD) achieved using this method were 0.30–2.50 ng/mL. The average recoveries ranged from 74.3% to 107% with relative standard deviation (RSD) between 2.6% and 15.7%. The material is characterized by low cost, simple preparation and good operability as a SPE filler. It can be extended to the detection of AGs in other food or agricultural samples.

Circulating tumor DNA (ctDNA) is a highly promising biomarker for the early diagnosis and treatment of gastric cancer (GC). However, there is still a lack of effective and practical ctDNA detection methods. In this work, a simple and economical capillary non-gel sieving electrophoresis-LED induced fluorescence detection (NGCE-LEDIF) platform coupled with catalytic hairpin assembly (CHA) as the signal amplification strategy is proposed for quantitative detection of PIK3CA E542K and TP53 (two types of ctDNA associated with GC). We have reasonably designed two pairs of programmable oligonucleotide hairpin probes for PIK3CA E542K and TP53. Using a one-pot reaction, the presence of ctDNA triggers the cyclic amplification of CHA, forming numerous thermodynamically stable H1/H2 double-strands. The H1/H2 double-stranded DNA catalyzed by PIK3CA E542K and TP53 can be easily separated by NGCE due to their different lengths, enabling simultaneous detection of both ctDNAs. Under optimal experimental conditions, the detection limits of this strategy for detecting GC-related biomarkers PIK3CA E542K and TP53 are 20.35 pM and 19.61 pM, respectively, and can achieve 730-fold signal amplification. This strategy has a good recovery in the serum matrix. The results of this study show that this strategy has significant advantages such as high selectivity, a simple process, no special instruments and equipment, no need for fluorescence modification of hairpin probes in advance, high automation, low cost, and minimal sample consumption. This provides a powerful method for the detection of trace cancer biomarkers in the serum matrix with good application prospects. [ABSTRACT FROM AUTHOR]

Multiplexed DNA target detection is of great significance in many fields including clinical diagnostics, environmental monitoring, biothreat detection and forensics. Although the emergence of DNA chip technology has accelerated this process, it is still a challenge to perform ultrasensitive DNA assay at low attomol concentrations so that DNA detection can be directly achieved without a PCR protocol. In this work, an oligonucleotide-functionalized silver nanoparticle tag has been successfully developed for multiplexed DNA electrochemical detection with ultrahigh sensitivity. The multiprobes containing oligo(d)A and the reporting probes were anchored onto the silver nanoparticles, followed by hybridizing with the silver nanoparticle conjugate modified with oligo(d)T. The hybridization-induced tag was found to show an aggregated nanostructure 10 times larger than the individual nanoparticle, as revealed by TEM. For sandwich-based assays, the tag was specifically coupled to a gold electrode surface via target DNA. Compared to a single nanoparticle label, this novel tag has shown excellent electroactive property and produces 103-fold amplification in the differential pulse voltammetric (DPV) method. Hepatitis B virus (HBV) sequence was employed as a sample model, and we have achieved a detection limit of 5 aM (~120 molecules in 40 [mu]L volume), demonstrating ultrasensitive measurement for DNA. The property of the electrochemical process involving silver aggregates was further investigated and the integrative oxidation of the silver tag was observed. We further demonstrated the multiplexed DNA target detection using array chips functionalized with Herpes simplex virus (HSV), Epstein--Barr virus (EBV) and cytomegalovirus (CMV) sequences, which shows effective recognition of the relative sequences individually or simultaneously. The method offers a uniquely new approach for DNA detection with ultrahigh sensitivity as well as advantages of rapidity, throughput, and miniaturization. 10.1021/ac101193e