Graphene quantum dots (GQD) with an average size of 3.1 nm were incorporated into a mesoporous porphyrinic zirconium-based metal−organic framework (MOF) by direct impregnation to render the donor−acceptor charge transfer from GQDs to porphyrinic linkers. The hybrid material still possesses around half porosity of the pristine MOF and shows a 100-fold higher electrical conductivity compared to that of the parent MOF. By utilizing the porphyrinic linkers as catalytically active units, the GQD− MOF material exhibits a better electrochemical sensing activity toward nitrite in aqueous solutions compared to both the pristine MOF and GQD.
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.
The effective and precise detection
of cancer and neurotransmitter
biomarkers including folic acid (FA), dopamine (DA), and epinephrine
(EP) are essential for early detection and diagnosis of cancer and
neurological disorders and for the development of new drugs. However,
it remains challenging to detect FA, DA, and EP with high selectivity
and sensitivity with a single material. Herein, we report a photoluminescence
(PL)-based selective sensing of FA, DA, and EP with nitrogen-doped
graphene quantum dots (NGQDs) synthesized from biocompatible chitosan
under ambient conditions using atmospheric pressure microplasmas.
By regulating the pH, the selective detection is achieved in broad
ranges from 0.8 to 80 μM for FA and 0.4 to 100 μM for
both DA and EP with the very low limits of detections of 81.7, 57.8,
and 16.7 nM for FA, DA, and EP, respectively. The developed PL sensing
method shows the high throughput of 5000 detections per hour. Moreover,
highly stable colloidal NGQD dispersion with 100 μg/mL concentration
for at least 100 PL detections is produced in 1 h by a single microplasma,
and the process is scalable. The mechanisms of the outstanding performance
are related to the enhanced, size-dependent π–π
stacking attraction between the NGQDs and the pH-regulated chemical
states of the analytes and the associated pH-specific photo-induced
electron transfer and PL.
Inflammatory diseases are some of the most common diseases in different parts of the world. So far, most attention has been paid to the role of environmental factors in the inflammatory process. The diagnosis of inflammatory changes is an important goal for the timely diagnosis and treatment of various metastatic, autoimmune, and infectious diseases. Graphene quantum dots (GQDs) can be used for the diagnosis of inflammation due to their excellent properties, such as high biocompatibility, low toxicity, high stability, and specific surface area. Additionally, surface-enhanced Raman spectroscopy (SERS) allows the very sensitive structural detection of analytes at low concentrations by amplifying electromagnetic fields generated by the excitation of localized surface plasmons. In recent years, the use of graphene quantum dots amplified by SERS has increased for the diagnosis of inflammation. The known advantages of graphene quantum dots SERS include non-destructive analysis methods, sensitivity and specificity, and the generation of narrow spectral bands characteristic of the molecular components present, which have led to their increased application. In this article, we review recent advances in the diagnosis of inflammation using graphene quantum dots and their improved detection of SERS. In this review study, the graphene quantum dots synthesis method, bioactivation method, inflammatory biomarkers, plasma synthesis of GQDs and SERS GQD are investigated. Finally, the detection mechanisms of SERS and the detection of inflammation are presented.
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