Carbon dots: Review of recent applications and perspectives in bio-sensing and biomarker detection

Carbon Dots (CDs) are carbon-based nanoparticles with relatively strong and tunable fluorescence emission properties and relatively good photo stability, which are increasingly used in sensing and biosensing as reported in hundreds of research publications. There are 4 types of CD-based sensors or detection (CD-only, CD-based Enzymatic, CD-based Antigen-Antibody modified, CD-based Nucleic acid biosensors) that will be described and compared in this review. Such analytical parameters as Limit of Detection (LOD), linear range, Relative Standard Deviation (RSD) are compared and discussed in this review. Median and/or average LOD, RSD, Linear Range are calculated and presented in multiple tables, while LODs are tabulated from 135 references. Among these biosensors, CD-based Nucleic Acid biosensors and CD-based Antibody-Antigen biosensors show better sensitivity (lower LOD) when compared with CD-only and CD-based Enzymatic biosensors. Four main groups of detection techniques applicable, such as fluorescence, electrochemical, colorimetry, and electrochemiluminescence methods are considered and compared for CD-based Antibody-Antigen biosensors descriptions. Perspectives of machine learning methods and smart phones as read out devices for CD-based bio-sensors are outlined in the conclusion of the review. We also briefly described and illustrated with graphic examples/figures some basic phenomena related to CD-based sensing, including CD doping, up-conversion, modification and immobilization of CDs, quenching and FRET.