Microplasma Band Structure Engineering in Graphene Quantum Dots for Sensitive and Wide-Range pH Sensing

Abstract

pH sensing using active nanomaterials is promising in many fields ranging from chemical reactions to biochemistry, biomedicine, and environmental safety especially in the nanoscale. However, it is still challenging to achieve nanotechnology-enhanced rapid, sensitive, and quantitative pH detection with stable, biocompatible, and cost-effective materials. Here, we report a rational design of nitrogen-doped graphene quantum dot (NGQD)-based pH sensors by boosting the NGQD pH sensing properties via microplasma-enabled band-structure engineering. Effectively and economically, the emission-tunable NGQDs can be synthesized from earthabundant chitosan biomass precursor by controlling the microplasma chemistry under ambient conditions. Advanced spectroscopy measurements and density functional theory (DFT) calculations reveal that functionality-tuned NGQDs with enriched −OH functional groups and stable and large Stokes shift along the variations of pH value can achieve rapid, label-free, and ionic-stable pH sensing with a wide sensing range from pH 1.8 to 13.6. The underlying mechanism of pH sensing is related to the protonation/ deprotonation of −OH group of NGQDs, leading to the maximum pH-dependent luminescence peak shift along with the bandgap broadening or narrowing. In just 1 h, a single microplasma jet can produce a stable colloidal NGQD dispersion with 10 mg/mL concentration lasting for at least 100 pH detections, and the process is scalable. This approach is generic and opens new avenues for nanographene-based materials synthesis for applications in sensing, nanocatalysis, energy generation and conversion, quantum optoelectronics, bioimaging, and drug delivery.

Graphdiyne Oxide Quantum Dots: The Enhancement of Peroxidase-like Activity and Their Applications in Sensing H2O2 and Cysteine

“…When the excitation wavelength changed from 371 to 451 nm, the photoluminescence (PL) peak shifted to a longer wavelength with the strongest peak excited at 411 nm (Figure a). The excitation-dependent PL behavior is commonly found in carbon-based quantum dots, which is probably due to the varying sizes of the prepared quantum dots. , Then, the PL emission spectra of the aqueous solutions of GDYO QDs and GDY with excitation at 411 nm were compared. The GDYO QDs showed emissions at 500 nm with a yellow-green hybrid luminescence showing significant quantum confinement effects, while GDY showed no detectable PL (Figure b).…”

Recent Advances in Inflammatory Diagnosis with Graphene Quantum Dots Enhanced SERS Detection

“…To avoid the use of high temperatures, Chiang’s group used microplasma technologies to synthesize colloidal NGQDs with a PLQY of 30% from chitosan at ambient conditions [ 59 ]. Various strategies involving plasma flow, reaction time, and the type of acid used to dissolve chitosan were employed to control the functionalities and thus the energy gap of the resulting NGQDs [ 59 , 60 ]. Another promising biomass waste as a GQD precursor is lignin, which consists of phenyl skeletons and oxygenated branches [ 61 ].…”

Regulation of multi-color fluorescence of carbonized polymer dots by multiple contributions of effective conjugate size, surface state, and molecular fluorescence

“…12–14 Similar to other fluorescent nanomaterials, such as semiconductor quantum dots (QDs) and noble metal nanoclusters, CDs possess interesting photoluminescence (PL) properties. 15–18 However, compared with the above fluorescent nanomaterials, CDs have the advantages of better biocompatibility and higher water-solubility, and wider sources of raw materials. 19–21…”

“…[12][13][14] Similar to other fluorescent nanomaterials, such as semiconductor quantum dots (QDs) and noble metal nanoclusters, CDs possess interesting photoluminescence (PL) properties. [15][16][17][18] However, compared with the above fluorescent nanomaterials, CDs have the advantages of better biocompatibility and higher water-solubility, and wider sources of raw materials. [19][20][21] For many potential applications of CDs such as in biosensing, bioimaging, and light emission, the synthesis of CDs with the emission in the long wavelength range is highly demanding.…”