Non-antibacterial carbon particles and its fluorescence properties

Owing to the distinctive morphologies, physiochemical characteristics and wide range of promising applications, carbon materials have become a hot topic in the history of modern nanoscience. Especially, researches in the field of biological applications involving carbon based materials raised a great attention due to its biocompatible physiognomies, chemical stability, high therapeutic outputs and optical absorptivity [1-3]. Carbon, being the most important structural element in human body is also referred to as a carbon-based life form. Henceforth, the utilization of carbon particles in clinical diagnostic and biological assays, can be a safer and simpler alternative for those cytotoxic, carcinogenic and costly synthetic dyes [4-5]. Here in this work, carbon particles are synthesized via a green chemistry approach using corn starch as the precursor. An environmental friendly hydrothermal technique was employed for the preparation of carbon particles (CP) without expending for any tedious purification processes. Also, a simultaneous reduction and functionalization of carbon particles are achieved using lime juice as a catalyst for hydrothermal carbonization. The structural and functional group modifications induced by the catalyst is studied via XRD, FTIR and SEM techniques. The obtained carbon nanoparticles (CP and CP-catalyst) revealed a broad diffraction peak in the range of 15-35° due to the (002) graphitic plane, indicating the occurrence of hydrothermal carbonization. A reduction in the oxygen functional group and Potassium functionalization of CP-catalyst was confirmed through FTIR analysis. SEM images illustrated that the particles are spherical in shape, but the catalyst treated CP exhibited well dispersability. The photoluminescence (PL) behaviour of both the samples was investigated and found an excellent luminescence with excitation independent and dependant properties. The PL lifetime analysis demonstrated that the CP-catalyst possess an enhanced emission decay time that aroused from the accelerated charge transfer process due to the potassium functionalization. As a prerequisite for the understanding of biocompatibility, the antibacterial activity of carbon particles against four bacteria Staphylococcus aureus, Bacillus subtilis, (Gram-positive) and Pseudomonas fluorescence, E. coli (Gram-negative) was further investigated using well-diffusion assay. As shown in Fig. 1 and Table 1, in either of the samples, biocidal activity against tested bacteria was not observed. Thus, the as-synthesized CP with excellent luminescence, good water solubility, high colloidal stability and non-antibacterial properties would be best suited for cell biological applications.   Fig 1: Antimicrobial activity of the test sample on Microorganisms A-Pseudomonas fluorescence; B- Staphylococcus aureus C-Bacillus subtilis; D- E. coli. Table1: Antimicrobial Activity of S1 and SL1 on Microorganisms   Staphylococcus aureus   Bacillus subtilis   Pseudomonas fluorescense E. coli   S1 0 0 0 0 SL1 0 0 0 0 DMSO 0 0 0 0