L-Tryptophan functionalized graphene quantum dots as a fluorescence indicator for pH detection in real water

Generating luminescent Graphene quantum Dots from Tryptophan: Fluorosensors for hydrogen peroxide in cancer cells

Herein, we report a single step synthesis of highly fluorescent Graphene Quantum Dots (GQDs) using tryptophan and glycerol as precursors via pyrolysis. The morphological and functional characterization of the prepared GQDs was performed using PXRD, FTIR, TEM, XPS and zeta potential measurements. The prepared GQDs found their practical application in ultrasensitive detection of an emerging potential cancer biomarker, H2O2, by exploiting the fluorescence quenching behaviour of H2O2. To evaluate the detection sensitivity, a series of various concentrations of H2O2 was spiked to biomatrices like, serum and MCF-7 (human breast cancer cell line) cell lysate medium. A remarkably low limit of detection (LOD) was found in serum medium (139.5 pM) which further improved in MCF-7 cell lysate medium (LOD 61.43 pM). Moreover, the sensing capacity of the GQDs was further validated in presence of various physiological variables such as glucose, cholesterol, insulin and nitrite. Sensing assay was also carried out in HaCaT (human keratinocyte cell line) cell lysate medium to compare the performance of our prepared sensor but the non-linearity of the F0/F versus H2O2 concentration plot pointed towards the conduciveness of the MCF-7 cell lysate medium for sensitive detection of H2O2.The mechanism behind the sensing was also explored using spectroscopic methods.

A neoteric dual-channel spectral sensor for wide-range pH detection based on variables in UV-vis peak and intensity

A water-soluble 2',4',6'-trihydroxy phenylazo luminol dye (THPL) with a D-π-A conjugated structure was developed for the first time for the dual-channel spectral sensing of a wide-range of pH values in aqueous solutions, using phloroglucinol as the electron-donating group, heterocycle amide luminol as the electron-accepting one and -NN- as the π-conjugated bridge. Its UV-vis absorption spectrum, especially its spectral response to pH, was investigated in detail. The results confirmed that the proposed THPL exhibited superior UV-vis spectral properties, a strong molar absorption coefficient (ε_max = 3.35 × 10⁴ L mol^-1 cm^-1) and a small half-band width of ca. 126 nm. In particular, either the absorption intensity (Abs) or peak (λ_max) changed linearly with pH values from 3.0 to 10.0 under the optimized conditions. Notably, THPL expressed an exclusive dual-channel spectral response to pH, i.e., Abs (a.u.) = 0.1316 + 0.0278 pH (R² = 0.9921), λ_max = 441.5 - 6.64 pH (R² = 0.9968, pH = 3.0-6.0) and λ_max = 359.6 + 7.38 pH (R² = 0.9879, pH = 6.0-10.0). Under the optimized conditions, THPL was applied to detect pH values in some aqueous and fruit juice samples with satisfactory results. The reversible recognition mechanism was deduced by UV-vis titration, ¹H NMR titration and theoretical calculation.

Do amino acid functionalization stratagems on carbonaceous quantum dots imply multiple applications? A comprehensive review

Amino acids are the noteworthy entity among biological molecules with diverse properties such as zwitterionic and amphoteric. Functionalizing carbon-based quantum dots using amino acids might be used for the extreme enhancement of electronic and optical properties of quantum dots and improve the performance of the resultant amino acid-functionalized quantum dots. The amino acid-functionalized quantum dots are highly soluble, sustainable, and biocompatible with virtuous optical and electrical performance, which makes them potential and suitable candidates for fabricating optoelectronic devices. The tenacity of using amino acids as functional groups to functionalize quantum dots and their novel properties are conferred to attain their multiple applications. The goal of this review is to provide the choices of amino acids based on the desired applications and a variety of functionalization techniques to make them a noteworthy material for future applications. The method of one-step and two-step functionalization strategies along with the properties of the resultant functionalized quantum dots and their plausible applications and future scope of the material are highlighted. Amidation is the basic principle behind the functionalization of quantum dots with amino acids. This review would be an exciting prospect to explore the pathways of the possible applications in different domains, in which the amino acid-functionalized quantum dots have not yet been explored. Further, this review article helps in pitching a variety of prominent applications right from sensors to energy storage systems either using the optical property or electronic property of amino acid-functionalized quantum dots.

Carbon Dots Conjugated with Vascular Endothelial Growth Factor for Protein Tracking in Angiogenic Therapy

One of the challenges of using growth factors for tissue regeneration is to monitor their biodistributions and delivery to injured tissues for minimally invasive detection. In the present study, tracking of human vascular endothelial growth factor (VEGF) was achieved by chemically linking it to photoluminescent carbon dots (CDs). Carbon dots were synthesized by the hydrothermal method and, subsequently, conjugated with VEGF using carbodiimide coupling. ELISA and western blot analysis revealed that VEGF-conjugated CDs preserve the binding affinity of VEGF to its antibodies. We also show that VEGF-conjugated CDs maintain the functionality of VEGF for tube formation and cell migration. The VEGF-conjugated CDs were also used for in vitro imaging of human umbilical vein endothelial cells. The results of this work suggest that cell-penetrating VEGF-conjugated CDs can be used for growth factor protein tracking in therapeutic and tissue engineering applications.