Luminol functionalized gold nanoparticles as colorimetric and chemiluminescent probes for visual, label free, highly sensitive and selective detection of minocycline

Electrochemical Biosensor for SARS-CoV-2 cDNA Detection Using AuPs-Modified 3D-Printed Graphene Electrodes

A low-cost and disposable graphene polylactic (G-PLA) 3D-printed electrode modified with gold particles (AuPs) was explored to detect the cDNA of SARS-CoV-2 and creatinine, a potential biomarker for COVID-19. For that, a simple, non-enzymatic electrochemical sensor, based on a Au-modified G-PLA platform was applied. The AuPs deposited on the electrode were involved in a complexation reaction with creatinine, resulting in a decrease in the analytical response, and thus providing a fast and simple electroanalytical device. Physicochemical characterizations were performed by SEM, EIS, FTIR, and cyclic voltammetry. Square wave voltammetry was employed for the creatinine detection, and the sensor presented a linear response with a detection limit of 0.016 mmol L-1. Finally, a biosensor for the detection of SARS-CoV-2 was developed based on the immobilization of a capture sequence of the viral cDNA upon the Au-modified 3D-printed electrode. The concentration, immobilization time, and hybridization time were evaluated in presence of the DNA target, resulting in a biosensor with rapid and low-cost analysis, capable of sensing the cDNA of the virus with a good limit of detection (0.30 µmol L-1), and high sensitivity (0.583 µA µmol-1 L). Reproducible results were obtained (RSD = 1.14%, n = 3), attesting to the potentiality of 3D-printed platforms for the production of biosensors.

Colorimetric Detection Based on Localized Surface Plasmon Resonance for Determination of Chemicals in Urine

Colorimetric sensors based on localized surface plasmon resonance (LSPR) have attracted much attention for biosensor and chemical sensor applications. The unique optical effect of LSPR is based on the nanostructure of noble metals (e.g., Au, Ag, and Al) and the refractive index of the environment surrounding these metal nanomaterials. When either the structure or the environment of these nanomaterials is changed, their optical properties change and can be observed by spectroscopic techniques or the naked eye. Colorimetric-probe-based LSPR provides a simple, rapid, real-time, nonlabelled, sensitive biochemical detection and can be used for point-of-care testing as well as rapid screening for the diagnosis of various diseases. Gold and silver nanoparticles, which are the two most widely used plasmonic nanomaterials, demonstrate strong and sensitive LSPR signals that can be used for the selective detection of several chemicals in biochemical compounds provided by the human body (e.g., urine and blood). This information can be used for the diagnosis of several human health conditions. This paper provides information regarding colorimetric probes based on LSPR for the detection of three major chemicals in human urine: creatinine, albumin, and glucose. In addition, the mechanisms of selective detection and quantitative analysis of these chemicals using metal nanoparticles are discussed along with colorimetric-detection-based LSPR for many other specific chemicals that can be detected in urine, such as catecholamine neurotransmitters, thymine, and various medicines. Furthermore, issues regarding the use of portable platforms for health monitoring with colorimetric detection based on LSPR are discussed.

Highly Stabilized Core-Satellite Gold Nanoassemblies in Vivo: DNA-Directed Self-Assembly, PEG Modification and Cell Imaging

Au nanoparticles (NPs) have important applications in bioimaging, clinical diagnosis and even therapy due to its water-solubility, easy modification and drug-loaded capability, however, easy aggregation of Au NPs in normal saline and serum greatly limits its applications. In this work, highly stabilized core-satellite Au nanoassemblies (CSAuNAs) were constructed by a hierarchical DNA-directed self-assembly strategy, in which satellite Au NPs number could be effectively tuned through varying the ratios of core-AuNPs-ssDNA and satellite-AuNPs-ssDNAc. It was especially interesting that PEG-functionalized CSAuNAs (PEG-CSAuNAs) could not only bear saline solution but also resist the enzymatic degradation in fetal calf serum. Moreover, cell targeting and imaging indicated that the PEG-CSAuNAs had promising biotargeting and bioimaging capability. Finally, fluorescence imaging in vivo revealed that PEG-CSAuNAs modified with N-acetylation chitosan (CSNA) could be selectively accumulate in the kidneys with satisfactory renal retention capability. Therefore, the highly stabilized PEG-CSAuNAs open a new avenue for its applications in vivo.

Cobalt(ii)-8-hydroxyquinoline-5-sulfonic acid complex/N-(4-aminobutyl)-N-ethylisoluminol/reduced graphene hybrids as nanocatalytic reaction platforms for chemiluminescence

The as-prepared Co^II(HQS)₂/ABEI/rGO hybrids exhibited excellent CL activity when reacted with hydrogen peroxide, the dissolved oxygen and periodate in alkaline solution.

Gold Triangular Nanoprisms and Nanodecahedra: Synthesis and Interaction Studies with Luminol toward Biosensor Applications

Gold triangular nanoprisms and nanodecahedra (pentagonal bipyramids) were synthesized in the absence and presence of nanoseeds by a simple solvothermal synthesis through the reduction of Auric Chloride (HAuCl₄) with poly(vinylpyrrolidone) (PVP) in N,N-dimethylformamide (DMF), respectively. These gold nanoparticles exhibit two plasmon resonance bands. The interaction of these gold nanoparticles with luminol was investigated using UV-vis and fluorescence spectroscopy since hefty number of environmental and biological sensors are based on the combination of luminol and gold nanoparticles. The gold nanoparticles quenches the fluorescence of luminol through a static quenching mechanism, i.e., ground state complex formation, which was confirmed by both absorption spectroscopy as well as time-resolved fluorescence spectroscopy. The Stern-Volmer quenching constant and the effective quenching constant determine that gold nanodecahedra has more interaction with luminol than that of triangular gold nanoprisms. The distance between the gold nanoparticles and luminol, calculated using FRET theory, is less than 8 nm, which indicates efficient energy transfer during interaction. These results are expected to be useful for the development of novel sensors.