Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures for sensitive and selective SARS-CoV-2 sensing.

The development of DNA-sensing platforms based on new synthetized Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures (AuNs), as a new pathway to develop a selective and sensitive methodology for SARS-CoV-2 detection is presented. A mixture of gold nanoparticles and gold nanotriangles have been synthetized to modify disposable electrodes that act as an enhanced nanostructured electrochemical surface for DNA probe immobilization. On the other hand, modified carbon nanodots prepared a la carte to contain Methylene Blue (MB-CDs) are used as electrochemical indicators of the hybridization event. These MB-CDs, due to their structure, are able to interact differently with double and single-stranded DNA molecules. Based on this strategy, target sequences of the SARS-CoV-2 virus have been detected in a straightforward way and rapidly with a detection limit of 2.00 aM. Moreover, this platform allows the detection of the SARS-CoV-2 sequence in the presence of other viruses, and also a single nucleotide polymorphism (SNPs). The developed approach has been tested directly on RNA obtained from nasopharyngeal samples from COVID-19 patients, avoiding any amplification process. The results agree well with those obtained by RT-qPCR or reverse transcription quantitative polymerase chain reaction technique.

Electrochemiluminescent nanostructured DNA biosensor for SARS-CoV-2 detection.

This work focuses on the development of an electrochemiluminescent nanostructured DNA biosensor for SARS-CoV-2 detection. Gold nanomaterials (AuNMs), specifically, a mixture of gold nanotriangles (AuNTs) and gold nanoparticles (AuNPs), are used to modified disposable electrodes that serve as an improved nanostructured electrochemiluminescent platform for DNA detection. Carbon nanodots (CDs), prepared by green chemistry, are used as coreactants agents in the [Ru(bpy)3]2+ anodic electrochemiluminescence (ECL) and the hybridization is detected by changes in the ECL signal of [Ru(bpy)3]2+/CDs in combination with AuNMs nanostructures. The biosensor is shown to detect a DNA sequence corresponding to SARS-CoV-2 with a detection limit of 514 aM.

Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2.

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron-hole pair generation in the space charge region in the TiO2-air interface and in the metal-semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron-hole recombination, a key factor in the enhancement of photo(electro)catalytic activity.