Effect of Lateral Size of Graphene Quantum Dots on Their Properties and Application

Abstract

Well-defined graphene quantum dots (GQDs) are crucial for their biological applications and the construction of nanoscaled optoelectronic and electronic devices. However, as-synthesized GQDs reported in many works assume a very wide lateral size distribution; thus, their apparent properties cannot truthfully reflect intrinsic properties of the well-defined GQDs, and more importantly, the applications of GQDs will be affected and limited as well. In this work, we demonstrated that different sized GQDs with a narrow size distribution could be obtained via gel electrophoresis of the crude GQDs prepared through a photo-Fenton reaction of graphene oxide (GO). It is illustrated that the photoluminesce (PL) emissions of the well-defined GQDs originated mainly from the peripheral carboxylic groups and conjugated carbon backbone planes through fluorescence and UV-vis spectroscopies. More importantly, our findings challenge the notion that the excitation wavelength dependent PL property of the as-synthesized GQDs is the intrinsic property of the size-defined GQDs. Preliminary data at the cellular level indicated that the small sized GQDs exhibit weaker quenching DNA dye ability but higher toxicity to the cells compared to that of the as-synthesized GQDs. This discovery is essential to explore applications of the GQDs in pharmaceutics and to understand the origin of the optoelectronic properties of GQDs.

Sorting Graphene Quantum Dots by Using Aluminum Ions

“…Mu and co‐workers also discovered that cellular internalization of GO coated with protein was size dependent . Our previous work also showed that smaller sized GQDs exhibited weaker ability to quench the fluorescence of small molecules . These results highlighted the need for high‐quality GQDs with well‐defined properties to facilitate their biomedical applications and to understand their properties.…”

“…However, aggregation between the reactants by the micelles was inevitable, which decreased the product yield. We recently discovered that gel electrophoresis was a very effective method that could be used to sort as‐prepared GQDs into different sizes, because the as‐prepared GQDs had peripheral carboxyl groups that were closely related to their sizes and charges . Three groups of differently sized GQDs with narrow size distributions could be obtained by gel electrophoresis, and each showed unique photoluminescence (PL) properties that were consistent with their sizes.…”

Graphene Oxide as an Optical Biosensing Platform: A Progress Report

“…In contrast, cellular uptake efficiency of the counterpart material with a negative surface charge is strongly modulated by lateral size. [42] Likewise, Mei et al, reported this size-dependent photoluminescent phenomenon. [39] In this context, GO could be utilized as a nanocarrier platform for small-interfering RNA (siRNA) delivery with interest also for future theranostic applications.…”

“…[42] Moreover, bi/few-layers GO microsheets that underwent gradual deoxygenation, via thermal reduction, led to GO with different oxygenated functional groups corresponding to different photoluminescent peaks as follows; the yellow-red emission of the studied GO (maximum peak at ≈610 nm) was mainly associated with epoxy/hydroxyl groups, whereas the blue emission (maximum peak at ≈500 nm) was mainly ascribed to the observed carbonyl functional groups. More in-depth research is required since oxidation grade in addition to layer numbers and lateral size should be carefully and systematically controlled.…”

“…Furthermore, they also observed that HeLa cells underwent changes in their microenvironment due to uptake of GO, eventually causing a relative cytotoxicity. [42] Copyright 2016, American Chemical Society. [26] It is worth to spot that another study reported that surface charge also plays a critical role in cellular uptake.…”