Aptamer/AuNPs encoders endow precise identification and discrimination of lipoprotein subclasses

DNA-functionalized gold nanoparticles: Modification, characterization, and biomedical applications

With the development of technologies based on gold nanoparticles (AuNPs), bare AuNPs cannot meet the increasing requirements of biomedical applications. Modifications with different functional ligands are usually needed. DNA is not only the main genetic material, but also a good biological material, which has excellent biocompatibility, facile design, and accurate identification. DNA is a perfect ligand candidate for AuNPs, which can make up for the shortcoming of bare AuNPs. DNA-modified AuNPs (DNA-AuNPs) have exciting features and bright prospects in many fields, which have been intensively investigated in the past decade. In this review, we summarize the various approaches for the immobilization of DNA strands on the surface of AuNPs. Representative studies for biomedical applications based on DNA-AuNPs are also discussed. Finally, we present the challenges and future directions.

Poly(N,N-dimethylacrylamide)-stabilized gold nanoparticles as nanozymes with enhancement of catalytic activity for detection of lomefloxacin

Recently, polymer-protected gold nanoparticles (AuNPs) have attracted extensive attention due to their good catalytic activities. However, how to regulate their catalytic activities by changing the polymer chain morphologies or the interactions between the ligands and the analytes through external stimuli is still a great challenge. This study describes a simple synthesis of AuNPs capped by thermo-responsive poly(N,N-dimethylacrylamide) (PDMAM). In comparison with three kinds of PDMAMs@AuNPs, PDMAM-2@AuNPs exhibited better peroxidase-mimic ability via the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with hydrogen peroxide (H₂O₂) to generate oxidized TMB (oxTMB). Interestingly, its catalytic activity could be regulated by changing environmental temperature. Importantly, the addition of the antibiotic lomefloxacin endowed the PDMAM-2@AuNPs with enhancement in catalytic efficiency due to electrostatic interactions and the increased levels of reactive oxygen species. Based on this principle, a protocol for highly selective and sensitive monitoring of lomefloxacin has been constructed with the color change from pale blue to deep blue. The ultraviolet-visible absorbance of oxTMB at the wavelength of 650 nm showed a good linear relationship with antibiotic concentration in the range of 0.25-10.0 µM (R² = 0.990). The limit of detection was 0.1 µM. The practical application of the proposed protocol with the promoted peroxidase-mimic activity for the measurement of lomefloxacin in capsules was realized.

Highly selective and sensitive detection of glutamate by an electrochemical aptasensor

An electrochemical aptamer-based sensor was developed for glutamate, the major excitatory neurotransmitter in the central nervous system. Determining glutamic acid release and glutamic acid levels is crucial for studying signal transmission and for diagnosing pathological conditions in the brain. Glutamic acid-selective oligonucleotides were isolated from an ssDNA library using the Capture-SELEX protocol in complex medium. The selection permitted the isolation of an aptamer 1d04 with a dissociation constant of 12 µM. The aptamer sequence was further used in the development of an electrochemical aptamer sensor. For this purpose, a truncated aptamer sequence named glu1 was labelled with a ferrocene redox tag at the 3'-end and immobilized on a gold electrode surface via Au-thiol bonds. Using 6-mercapto-1-hexanol as the backfill, the sensor performance was characterized by alternating current voltammetry. The glu1 aptasensor showed a limit of detection of 0.0013 pM, a wide detection range between 0.01 pM and 1 nM, and good selectivity for glutamate in tenfold diluted human serum. With this enzyme-free aptasensor, the highly selective and sensitive detection of glutamate was demonstrated, which possesses great potential for implementation in microelectrodes and for in vitro as well as in vivo monitoring of neurotransmitter release.