Real-time kinetic analysis and detection of glycated hemoglobin A1c using a quartz crystal microbalance-based aptasensor.

Glycated hemoglobin (HbA1c) has been an important biomarker for long-term diagnosis and monitoring of diabetes mellitus. The development of a rapid, reliable, and less sophisticated device to measure HbA1c is imperative to facilitate efficient early-care diabetes management. To date, no existing aptamer-based biosensor (aptasensor) for detecting HbA1c has been developed using a quartz crystal microbalance (QCM). In this study, the aptamer specific to HbA1c as a novel biosensing receptor was covalently functionalized onto a QCM substrate via mixed self-assembled monolayers (SAMs). A portable QCM equipped with a liquid-flow module was used to investigate the biospecificity, sensitivity, and interaction dynamics of the aptamer functionalized surfaces. The real-time kinetic analysis of HbA1c binding to the surface-functionalized aptamers revealed "on" and "off" binding rates of 4.19 × 104 M-1 s-1 and 2.43 × 10-3 s-1, respectively. These kinetic parameters imply that the QCM-based aptasensor specifically recognizes HbA1c with an equilibrium dissociation constant as low as 57.99 nM. The linear detection of HbA1c spanned from 13 to 108 nM, with a limit of detection (LOD) of 26.29 nM. Moreover, the spiked plasma sample analysis offered compelling evidence that this aptasensor is a promising technique for developing a point-of-care device for diabetes mellitus.

Paper-based scanometric assay for lead ion detection using DNAzyme.

A facile and simple paper-based scanometric assay was developed to detect Pb(2+) using GR5-DNAzyme. Magnetic beads (MBs) and gold nanoparticles (AuNPs) were used as a signal collector and a signal indicator, respectively. They were linked together by GR5-DNAzyme, comprising an enzyme and a substrate strand pairing up with each other. In the presence of Pb(2+), the substrate strand is cut into two pieces, resulting in the disassembly of AuNPs from the MBs. These AuNPs were spotted on predefined areas on a chromatography paper, where signal is amplified through silver reduction. This sensing platform exhibits high sensitivity and selectivity toward Pb(2+), giving a detection limit of 0.3 nM and a linear fitting range from 0.1 to 1000 nM. Testing of this biosensor in river water and synthetic urine samples also showed satisfying results. Besides offering simultaneous and multi-sample analysis, this paper-based sensing platform presented here could be potentially applied and served as a general platform for on-site, naked eyes, and low-cost monitoring of other heavy metal ions in environmental and body fluid samples.