Excitation-Independent Blue-Emitting Carbon Dots from Mesoporous Aminosilica Nanoreactor for Bioanalytical Application

Here we present the first example of excitation-independent blue-emitting carbon dots (iC-dots) obtained by pyrolysis of citric acid (CA) without post-treatment chromatographic separation. To confine the growth and shape of carbon nanoparticles, silica gel with immobilized aminopropyl groups (SiO₂–NH₂) was used as a nanoreactor. It was demonstrated that the carbonization of SiO₂–NH₂ with embedded CA resulted in the formation of unbound wC-dots and immobilized iC-dots. Because of their firm attachment to the surface, iC-dots can be easily separated from low-molecular impurities and wC-dots by simply rinsing the nanocomposite with water. From atomic force and transmission electron microscopies iC-dots can be represented as flattened spheroids with 2–4 nm of height and 5 nm in lateral size. The size distribution profile for wC-dots is very wide with about 95% the particles within the 2.5–5.5 nm size range. Increasing the template pore size from 4.9 up to 9.1 nm has no effect on the size of the iC-dots. From Fourier transform infrared analysis and X-ray photoelectron spectroscopy data it was assumed that iC-dots belong to N-doped C-nanoparticles with 9:1 carbon to nitrogen atomic ratio. As-prepared iC-dots demonstrate excitation-independent photoluminescence at 445 nm with quantum yields up to 16.8%, which makes them attractive for bioanalytical application.