An ultrasensitive label-free assay of 8-hydroxy-2'-deoxyguanosine based on the conformational switching of aptamer.

We developed a highly sensitive label-free assay of 8-hydroxy-2'-deoxyguanosine (8-OHdG) using 8-OHdG-aptamer (Apt) as the recognition element. The Apt was adsorbed onto the surface of gold nanoparticles (AuNPs), which prevents them from aggregating under high-salt conditions. Upon addition of 8-OHdG, the conformation of the Apt changes to form a G-quadruplex structure, which leads to the aggregation of the AuNPs along with the increase of the resonance light scattering intensity. The mechanism of 8-OHdG that induces Apt to form G-quadruplexes structure was studied by circular dichroism. The response signals linearly correlated with the concentration of 8-OHdG ranging from 90.8pM to 14.1nM with a detection limit of 27.3pM, which is much lower than that obtained by other methods. This method does not need any label steps and sophisticated equipment. The application for detection of 8-OHdG in real samples further demonstrated its reliability. This strategy would be helpful for developing a universal analytical method by simply replacing corresponding aptamers for various target molecules.

Fluorescence quenching determination of metallothioneins using 8-hydroxyquinoline-5-sulphonic acid-Cd(II) chelate.

A novel method for the determination of metallothioneins (MTs) in urine was developed by fluorescence quenching strategy. The response signals linearly correlated with the concentration of MTs in the ranges of 3.12×10(-8)-1.23×10(-6) mol L(-1), and the limit of detection (LOD) was 9.36×10(-9) mol L(-1). The proposed method avoids the label and derivatization steps in common methods, and is reliable, inexpensive and sensitive. Furthermore, the interaction of MTs and 8-hydroxyquinoline-5-sulphonic acid (HQS)-Cd(II) chelate was investigated, and a static quenching mode was proposed to be primarily responsible for the fluorescence quenching event. It could provide a promising potential for the detection of the biomacromolecules which have no native fluorescence, and be benefit to extend the application of fluorescence strategy.

Colorimetric detection of metallothioneins using a thymine-rich oligonucleotide-Hg complex and gold nanoparticles.

A simple and sensitive method for label-free, colorimetric detection of metallothioneins (MTs) has been developed by using a thymine (T)-rich oligonucleotide (TRO)-Hg-AuNP system. In this colorimetric strategy, the thiol groups of MTs could interact with mercury from the T-Hg(2+)-T complex to release TRO, resulting in a color change of the system. The response signals linearly correlated with the concentration of MTs over the range of 2.56 × 10(-8) to 3.08 × 10(-7) mol L(-1), and the limit of detection was 7.67 × 10(-9) mol L(-1). The relative standard deviation and the recovery were 2.3-4.8% (n = 11) and 94.2-103.9%, respectively. The proposed method avoids the label and derivatization steps in common methods, allows direct analysis of the samples by the naked eye without costly instruments, and is reliable, inexpensive, and sensitive.

Resonance light scattering determination of metallothioneins using levofloxacin-palladium complex as a light scattering probe.

A novel method of resonance light scattering (RLS) was developed for the analysis of trace metallothioneins (MTs) in human urine. In a CH(3)COOH-CH(3)COONa buffer solution of pH 4.5, the formation of a complex between levofloxacin (LEV)-Pd and MTs led to enhance the RLS intensity of the system, and the enhanced RLS intensity at 468 nm was proportional to the concentration of MTs in the range of 0.059-22.4 µg mL(-1). The linear regression equation was ΔI=127.5 ρ (µg mL(-1))-88.02 with a correlation coefficient of 0.9992, and the detection limit of 17.8 ng mL(-1). The relative standard deviation and the average recovery were 3.8-5.4% (n=11) and 92.15%, respectively. The proposed method is convenient, reliable and sensitive, and has been used successfully for the determination of trace MTs in human urine samples.