Improving the biocompatibility of carbon nanodots for cell imaging

Assessing the efficacy of carbon nanodots derived from curcumin on infectious diseases

INTRODUCTION

The threat of new, emerging, and multidrug-resistant microbes is increasing which has created the necessity for new antimicrobials. In this regard, nanotechnology can be an alternative for the treatment of infectious microbes. Curcumin has been used since ancient times as antimicrobials; however, it has limitations due to its less aqueous solubility, bioavailability, and biocompatibility. This problem can be solved by curcumin-derived carbon nanodots which are emerging antimicrobials of <10 nm size, water-soluble, biocompatible, less toxic, and fluorescent.

AREA COVERED

The review discusses the application of curcumin-derived carbon nanodots against various pathogenic microbes including bacteria and dreaded viruses like SARS-CoV-2. In addition, the role of curcumin carbon nanodots in biolabelling of pathogenic microbes, mechanism of action, bioimaging, and therapy has been critically examined.

EXPERT OPINION

Carbon nanodots play an important role in combating pathogenic microbes by early diagnosis, bioimaging, nanocarrier for antimicrobial drugs, and therapy of infectious diseases. Curcumin carbon nanodots have already demonstrated their benefits of being water soluble, bioavailable, and biocompatible. However, more thorough research is needed to understand the efficacy and safety of curcumin carbon nanodots. In the future, curcumin-derived carbon nanodots can be used as alternative antimicrobial agents to fight microbial infections including multidrug-resistant microbes.

Precise regulation of the properties of hydrophobic carbon dots by manipulating the structural features of precursor ionic liquids

To prepare carbon dots (CDs), there are numerous protocols that use a wide variety of carbon sources, which results in properties of CDs that are unpredictable and highly variable. Therefore, the development of reliable approaches for precisely regulating the nature of CDs is urgently required. Herein, a series of organophilic/hydrophobic CDs (OCDs) were prepared under microwave agitation with ionic liquid 1-alkyl-3-methylimidazolium dicyanamide as the precursor, by varying the alkyl chain linked in the cationic imidazolium moiety. The physicochemical, optical and biological properties, and imaging performance of OCDs were exploited to elucidate the structure-activity relationship, and it was discovered that the alkyl chain plays key roles in governing the properties of OCDs. The increase in the alkyl chain length, from ethyl, butyl, hexyl, and octyl to decyl, led to a remarkable variation in the properties of the OCDs, i.e., a reduction in nitrogen doping from 40.71 to 20.75%, a decrease in binding affinity with bovine serum albumin (BSA), and an increase in cytotoxicity. The interaction of OCDs with BSA and the formation of a 'protein corona' substantially increased the biocompatibility of the OCDs. The OCDs penetrated into MCF-7 human breast cancer cells in 10 min and demonstrated bright fluorescence imaging.

Zwitterionic carbon dot-encapsulating pH-responsive mesoporous silica nanoparticles for NIR light-triggered photothermal therapy through pH-controllable release

Here, we designed a pH-responsive Indocyanine Green (ICG)-loaded zwitterionic fluorescent carbon dot (CD)-encapsulating mesoporous silica nanoparticle (MSN) for pH-tunable image-guided photothermal therapy.

Detection of yeast Saccharomyces cerevisiae with ionic liquid mediated carbon dots

Hydrophobic nitrogen-doped carbon dots are prepared with energetic ionic liquid (1,3-dibutylimidazolium dicyandiamide, BbimDCN) as carbon source. A yield of as high as 58% is obtained for the carbon dots, shortly termed as BbimDCN-OCDs, due to the presence of thermal-instable N(CN)₂^- moiety. BbimDCN-OCDs exhibit favorable biocompability and excellent imaging capacity for fluorescence labelling of yeast cell Saccharomyces cerevisiae. In addition, chitosan-modified Dy³⁺-doped magnetic nanoparticles (shortly as Chitosan@Fe_2.75Dy_0.25O₄) with superparamagnetism are prepared. The electrostatic attraction between positively charged magnetic nanoparticles and negatively charged yeast cells facilitates exclusive recognition/isolation of S. cerevisiae. In practice, S. cerevisiae is labelled by BbimDCN-OCDs and adhered onto the Chitosan@Fe_2.75Dy_0.25O₄. The yeast/ BbimDCN-OCDs/Chitosan@Fe_2.75Dy_0.25O₄ composite is then isolated with an external magnet and the fluorescence from BbimDCN-OCDs incorporated in S. cerevisiae is monitored. The fluorescence intensity is linearly correlated with the content of yeast cell, showing a calibration graph of F = 3.01log[C]+11.7, offering a detection limit of 5×10² CFU/mL. S. cerevisiae content in various real sample matrixes are quantified by using this protocol.

Understanding the Capsanthin Tails in Regulating the Hydrophilic-Lipophilic Balance of Carbon Dots for a Rapid Crossing Cell Membrane

Here we use natural Chinese paprika to prepare a new kind of amphiphilic carbon dot (A-Dot) that exhibits bright, multicolored fluorescence and contains hydrophilic groups as well as lipophilic capsanthin tails on the surface. It is found that the capsanthin tails in a phospholipid-like structure can promote cell internalization of the A-Dots via crossing cell membranes rapidly in an energy-independent fashion. Compared to highly hydrophilic carbon dots (H-Dots), a control sample prepared from the microwave thermolysis of citric acid and ethylenediamine, our synthesized A-Dots can be taken up by CHO, HeLa, and HFF cells more easily. More importantly, we develop a method to calibrate the hydrophilic-lipophilic balance (HLB) values of various kinds of carbon dots (C-Dots). HLB values of A-Dots and H-Dots are determined to be 6.4 and 18.4, respectively. Moreover, we discover that the cellular uptake efficiency of C-Dots is closely related to their HLBs, and the C-Dots with an HLB value of around 6.4 cross the cell membrane easier and faster. As we regulate the HLB value of the A-Dots from 6.4 to 15.3 by removing the capsanthin tails from their surfaces via alkali refluxing, it is found that the refluxed A-Dots can hardly cross HeLa cell membranes. Our work is an essential step toward understanding the importance of regulating the HLB values as well as the surface polarity of the C-Dots for their practical use in bioimaging and also provides a simple but effective way to judge whether the C-Dots in hand are appropriate for cell imaging.

Hydrophobic Carbon Nanodots with Rapid Cell Penetrability and Tunable Photoluminescence Behavior for in Vitro and in Vivo Imaging

Tunable fluorescent emission and applications in both in vitro and in vivo imaging of hydrophobic carbon nanodots (CNDs) with rapid penetration capability are reported. The hydrophobic CNDs are prepared via hydrothermal treatment of ionic liquid 1-ethyl-3-methylimidazolium bromide and exhibit excitation-dependent photoluminescence behavior along with a red-shift in the excitation/emission maxima with concentration. The quantum yields of the as-prepared CNDs are in the range of 2.5-4.8% at an excitation wavelength of 300-600 nm. The rapid penetration behavior (within 1 min) of CNDs into the cell membrane significantly reduces the sample treatment time and avoids potential fluorescence quenching induced by the interaction between CNDs and samples. A co-location study reveals that the hydrophobic CNDs are distributed mainly in the lysosome. The potentials of the hydrophobic CNDs as fluorescent probe in in vitro and in vivo imaging are well demonstrated by the labeling of HeLa cells, MCF-7 cells, A549 cells, and Kunming mice.