Carbon dots (CDs) possess unique optical properties such as tunable photoluminescence (PL) and excitation dependent multicolor emission. The quenching and recovery of the fluorescence of CDs can be utilized for detecting analytes. The PL mechanisms of CDs have been discussed in previous articles, but the quenching mechanisms of CDs have not been summarized so far. Quenching mechanisms include static quenching, dynamic quenching, Forster resonance energy transfer (FRET), photoinduced electron transfer (PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). Following an introduction, the review (with 88 refs.) first summarizes the various kinds of quenching mechanisms of CDs (including static quenching, dynamic quenching, FRET, PET and IFE), the principles of these quenching mechanisms, and the methods of distinguishing these quenching mechanisms. This is followed by an overview on applications of the various quenching mechanisms in detection and imaging.

The quenching of the fluorescence of carbon dots: A review on mechanisms and applications

Carbon quantum dots (CQDs) as an emerging class of quantum dots (QDs) with advantages such as good photoluminescence (PL) properties, easy synthesis routes, economical synthesis, cheap starting materials, water-solubility, low levels of toxicity, chemical stability, and easy functionalization have received great attention during recent years. CQDs have been used in versatile sensor applications. CQD sensors could be ultimately sensitive, and the limit of detection (LOD) for these sensors can reach the nanomolar, picomolar or even femtomolar ranges. CQD-based sensors and biosensors work with different mechanisms including fluorescence quenching, static quenching, dynamic quenching, energy transfer, inner filter effect (IFE), photo-induced electron transfer (PET), and fluorescence resonance energy transfer (FRET). CQD-based sensors and biosensors have been applied for the detection of different species such as metal ions, acids, proteins, biothiols, polypeptides, DNA and miRNA, water pollutants, hematin, drugs, vitamins, and other chemicals. It seems that CQD-based sensors and biosensors are promising candidates for high performance and yet accurate sensors in different areas. In this review, CQDs are introduced, and the synthesis methods and optical properties of CQDs are discussed. Different types of CQD-based sensors and biosensors and their working mechanisms are clarified.

Principles, mechanisms, and application of carbon quantum dots in sensors: a review

Personal protective equipment (PPE) is critical to protect healthcare workers (HCWs) from highly infectious diseases such as COVID-19. However, hospitals have been at risk of running out of the safe and effective PPE including personal protective clothing needed to treat patients with COVID-19, due to unprecedented global demand. In addition, there are only limited manufacturing facilities of such clothing available worldwide, due to a lack of available knowledge about relevant technologies, ineffective supply chains, and stringent regulatory requirements. Therefore, there remains a clear unmet need for coordinating the actions and efforts from scientists, engineers, manufacturers, suppliers, and regulatory bodies to develop and produce safe and effective protective clothing using the technologies that are locally available around the world. In this review, we discuss currently used PPE, their quality, and the associated regulatory standards. We survey the current state-of-the-art antimicrobial functional finishes on fabrics to protect the wearer against viruses and bacteria and provide an overview of protective medical fabric manufacturing techniques, their supply chains, and the environmental impacts of current single-use synthetic fiber-based protective clothing. Finally, we discuss future research directions, which include increasing efficiency, safety, and availability of personal protective clothing worldwide without conferring environmental problems.

Sustainable Personal Protective Clothing for Healthcare Applications: A Review.

Can graphene take part in the fight against COVID-19?

An overview of functional nanoparticles as novel emerging antiviral therapeutic agents.

Developing nanomaterials-based antimicrobial agents has shown a widespread promise. In this study, silver nanoparticle-modified graphene oxide (GO-AgNPs) nanocomposites were self-assembled via inte...

Antiviral Activity of Graphene Oxide–Silver Nanocomposites by Preventing Viral Entry and Activation of the Antiviral Innate Immune Response

Interaction between fluorescein isothiocyanate and carbon dots: Inner filter effect and fluorescence resonance energy transfer.

Carbon dots (CDs) have demonstrated attractive potential in cell imaging and tracking However, one of the most challenge problems is the selective entrance of CDs into the cytoplasm or cell nucleus Here, a facile strategy was developed to prepare two types of CDs capable of selective entrance into cytoplasm and the whole cell without further surface modification The surface charge of CDs changes from negative to neutral after the addition of urea in the hydrothermal process, and the as-prepared CDs exhibit different fluorescent colors The blue-fluorescent CDs (b-CDs) can only enter the cytoplasm, while the cyan-fluorescent CDs (c-CDs) can distribute over the whole cell, including the nucleus Additionally, the antiviral activity of the two CDs against pseudorabies virus (PRV) was studied and b-CDs were shown to have better antiviral activity This study has provided a facile and novel strategy for the fabrication of CDs used in selective cell imaging, which may facilitate the application of CDs in nanomedicine

/pdf/blue-and-cyan-fluorescent-carbon-dots-one-pot-synthesis-adgeoj4qx1.pdf

Blue and cyan fluorescent carbon dots: one-pot synthesis, selective cell imaging and their antiviral activity

Glutathione (GSH) is an important antioxidant and plays crucial roles in basic biological functions. Thus far, it still remains a challenge to develop convenient and reliable ways to quantify and monitor the changes in bodily GSH levels. Herein, we have developed a simple, sensitive, and label-free fluorescence resonance energy transfer (FRET)-based probe for GSH with MnO2 nanosheets as an energy acceptor and silica coated CdSe/ZnS quantum dots (QDs) as the energy donor. The in situ synthesis of MnO2 nanosheets allowed the direct formation of QDs@SiO2@MnO2 nanocomposites, and enabled the occurrence of FRET with the donor fluorescence to be quenched. Upon the addition of GSH, MnO2 nanosheets were decomposed, and QDs@SiO2 nanobeads were released with a remarkable recovery of the fluorescence intensity in a target-dependent manner. The established FRET probe showed excellent selectivity and sensitivity towards GSH. The feasibility of the probe for GSH detection in a complex matrix was further investigated by analyzing the GSH content in reduced glutathione tablets. The results indicated the capability of the probe to detect low concentrations of GSH and suggested the practicability of the probe for GSH determination in real samples.

A sensitive label-free FRET probe for glutathione based on CdSe/ZnS quantum dots and MnO2 nanosheets

A ratiometric probe for determining ferric ions (Fe3+) was developed based on nitrogen-doped carbon dots (CDs) and rhodamine B isothiocyanate (RhB), which was then applied to selective detection of Fe3+ in PB buffer solution, lake water, and tap water. In the sensing system, FePO4 particles deposit on the surface of CDs, resulting in larger particles and surface passivation. The fluorescence (FL) intensity and the light scattering (LS) intensity of CDs can be gradually enhanced with the addition of Fe3+, while the FL intensity of RhB remains constant. The ratiometric light intensity of CDs LS and RhB FL was quantitatively in response to Fe3+ concentrations in a dynamic range of 0.01–1.2 μM, with a detection limit as low as 6 nM. Other metal ions, such as Fe2+, Al3+, K+, Ca2+, and Co2+, had no significant interference on the determination of Fe3+. Compared with traditional probes based on single-signal probe for Fe3+ detection, this dual-signal-based ratiometric probe exhibits a more reliable and stable response on target concentration and is characterized by easy operation in a simple fluorescence spectrophotometer.

/pdf/a-novel-ratiometric-probe-based-on-nitrogen-doped-carbon-463wa0plz6.pdf

Lingzhi Liu

Papers

Antiviral Activity of Graphene Oxide–Silver Nanocomposites by Preventing Viral Entry and Activation of the Antiviral Innate Immune Response

Interaction between fluorescein isothiocyanate and carbon dots: Inner filter effect and fluorescence resonance energy transfer.

Blue and cyan fluorescent carbon dots: one-pot synthesis, selective cell imaging and their antiviral activity

A sensitive label-free FRET probe for glutathione based on CdSe/ZnS quantum dots and MnO2 nanosheets

A Novel Ratiometric Probe Based on Nitrogen-Doped Carbon Dots and Rhodamine B Isothiocyanate for Detection of Fe3+ in Aqueous Solution