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.

Resonance light scattering determination of uranyl based on labeled DNAzyme-gold nanoparticle system.

A resonance light scattering (RLS) method has been developed using a uranyl (UO2(2+)) specific DNAzyme and gold nanoparticles (AuNPs). In this strategy, the cleavage of the substrate strand (SDNA) of DNAzyme results in releasing a shorter duplex in the presence of UO2(2+), leading to the aggregation of AuNPs and the increase of RLS intensity. The response signals linearly correlated with the concentration of UO2(2+) over the range of 1.36×10(-8)-1.50×10(-7) mol L(-1). The limit of detection (LOD) is 4.09×10(-9) mol L(-1). The method has excellent selectivity and higher sensitivity. It could provide a promising potential for the detection of metal ions, and be benefit to extend the application of RLS method.

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.

Improvement of expression level and bioactivity of soluble tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) by a novel zinc ion feeding strategy.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (Apo2L/TRAIL) is a new member of the TNF superfamily. In this work, the key role of Zn(2+) in high-level expression of soluble TRAIL was confirmed. The yield of soluble TRAIL reached 1.6 g l(-1) using a novel, two-stage Zn(2+) feeding strategy, and the accumulation of TRAIL inclusion bodies decreased. Furthermore, the purified TRAIL showed stronger cytotoxicity activity against human pancreatic 1990 tumor cells as the molar ratio of Zn(2+) to TRAIL monomer was 2 in purified TRAIL solution.