We report the production of multicolor-emissive carbon dots via hydrothermal synthesis that is stable, cost-effective, and bio-compatible for localized photothermal heating (by light-to-heat conversion) of biological assays. We analyze the effect of the carbon dot synthesis protocol (temperature and pH) on the resulting bandgap energies to yield nanoparticles with tunable optical and thermal properties. Results showed a significantly higher photothermal conversion in red color-emitting carbon dots compared to their blue, cyan, green, and yellow counterparts. The underlying mechanism of enhanced photothermal conversion efficiency is explained due to the high-frequency electron-phonon coupling in engineered carbon dots with smaller HUMO and LUMO bandgaps. This phenomenon (similar to localized surface plasmon resonance in metallic nanoparticles) initiates a thermal vibration in the carbon dot lattice which eventually dissipates as localized heat. Optimized for this effect, we show that these engineered carbon-based nanoparticles can yield high-temperature ramp rates (~11 °C/s) when illuminated with a blue laser (~300mW). We harnessed these suspended carbon dots in a nanoparticle solution containing polymerase chain reaction (PCR) assay to achieve ultrafast thermocycling to amplify a target ~230 bp DNA sequence in &lt;10 minutes. Results from these studies can potentially lead to the development of rapid and portable PCR thermocyclers that operate by non-contact heating.

Bandgap engineering of carbon-based nanoparticles enables efficient photothermal PCR for rapid and portable medical diagnostics

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ACS Spring 2023

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