A label-free and
enzyme-free colorimetric sensor for rapid detection
of Pb2+ is reported, which is based on the strategy of
DNAzyme-mediated RNA cleavage combined with an annealing-accelerated
DNA hybridization chain reaction (HCR). As a trigger DNA, the substrate
strand (STM) of DNAzyme can initiate HCR effectively. However,
when it is cleaved by DNAzyme in the presence of Pb2+,
the separation of DNA functional domains leads to a serious decrease
in HCR efficiency. As a result, the difference in Pb2+ concentration
converts into the difference of DNA assembly, which eventually leads
to the color change of colloidal gold nanoparticles (AuNPs). In this
work, a DNA strand (cGR5) completely complementary to the catalytic
strand (GR5) of DNAzyme is used to improve the dissociation of STM to enhance the HCR efficiency. In addition, the simple operation
of DNA annealing is first used to accelerate the HCR process, enabling
the Pb2+ detection to be completed in about 30 min. As
advantages of high sensitivity, good selectivity, strong anti-interference
ability, and good practical performance are achieved, it is anticipated
that the cheap and simple colorimetric sensor will be helpful for
on-site detection of environmental and food samples.
A novel, Ω-shaped fiber-optic localized surface plasmon resonance (FOLSPR) biosensor was designed for sensitive real-time and label-free bacterial detection. The designed Ω-shaped fiber-optic probe exhibits an outstanding sensitivity, due to the effect of unique geometry on performance. The results show that refractive index (RI) sensitivity of the Ω-shaped fiber-optic probe is 14 times and 2.5 times higher than those of the straight-shaped and the Ushaped FOLSPR, respectively. In addition, the reason for the geometry and the bending radius effects on RI sensitivity was discussed by investigating the relationship between RI sensitivity and the bending area. The results show that RI sensitivity was enhanced with the increase of bending area, and the best RI sensitivity obtained by Ω-shaped FOLSPR was 64.582 (a.u.)/RIU. Combined with this newly designed Ω-shaped FOLSPR biosensor, a real-time, label-free, sensitive, and highly selective bacterial detection method was established. In this work, the aptamers immobilized on the surface of FOLSPR could specifically capture Salmonella Typhimurium, resulting in an intense change of the absorption peak. In line with this principle, the FOLSPR biosensor achieved high detection sensitivity for Salmonella Typhimurium down to 128 CFU/mL within a linear range from 5 × 10 2 to 1 × 10 8 CFU/mL and showed good selectivity for Salmonella Typhimurium detection compared to other bacteria. Furthermore, the FOLSPR biosensor was successfully applied to the detection of Salmonella Typhimurium in a chicken sample with the recoveries of 85−123%. With these characteristics, the novel biosensor is a potential alternative tool in food analysis and environmental monitoring.
Background
Retinol binding protein 4 (RBP4) has been regarded as an important serological biomarker for type 2 diabetes mellitus (T2DM). Hence, the construction of a highly sensitive detection method for RBP4 is the key to early prevention and multidisciplinary intervention of T2DM. In this work, a dual-quenched electrochemiluminescence (ECL) immunosensor has been fabricated for ultrasensitive detection of RBP4 by combining zeolitic imidazolate framework-67/AuPt-supported luminol (luminol@AuPt/ZIF-67) with MnO2 nanosheets-grown on carbon nanotubes (MnO2@CNTs).
Results
AuPt/ZIF-67 hybrids with high-efficiency peroxidase-like activity could provide multipoint binding sites for luminol and antibodies and significantly boost the amplified initial signal of the ECL immunosensor. Upon glutathione/H2O2 coreactants system, MnO2@CNTs composites could quench the initial signal by inhibiting mimic peroxidase activity of luminol@AuPt/ZIF-67. Moreover, the absorption spectrum of the MnO2@CNTs composites completely overlaps with the emission spectrum of luminol, which can further reduce initial signal by ECL resonance energy transfer (ECL-RET).
Conclusions
Benefiting from the above-mentioned properties, the designed immunoassay sensitivity exhibited excellent sensitivity and relative stability for RBP4 detection range from 0.0001 to 100 ng mL−1 with a low detection limit of 43 fg mL−1. Therefore, our ECL immunosensor provides an alternative assaying strategy for early diagnosis of T2DM.
Graphic abstract
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