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In this paper, the study of surface modification of two-dimensional (2D), non-luminescent CdS nanoplates (NPLs) by thiol-containing ligands is presented. We show that a process of twophase transfers with appropriate ligand exchange transforms non-luminescent NPLs into spherical CdS nanoparticles (NPs) exhibiting a blue photoluminescence with exceptionally high quantum yield ~90%. In the process, transfer from inorganic solvent to water is performed, with appropriately selected ligand molecules and pH values (forward phase transfer), which produces NPs with modified size and shape. Then, in reverse phase transfer, NPs are transferred back to toluene due to surface modification by combined Cd (OL) 2 and Cd (Ac) 2 . As a result, spherical NPs are formed (average diameter between 4 and 6 nm) with PL QY as high as 90%. This is unique for core only CdS NPs without inorganic shell.

The results presented in this paper show how the optical properties and colloidal stability of quantum dots (QDs) vary depending on pH conditions. For this investigation, as-synthesized hydrophobic CdSe/CdS QDs were transferred to an aqueous medium by surface modification with 3-mercaptopropionic acid. The ligand exchange procedure was applied under three different pH conditions: acidic, neutral and alkaline, to obtain three kinds of hydrophilic QDs dispersed in phosphate buffer. The efficiency of the functionalization of QDs was estimated based on the changes in ABS and the highest value was obtained under acidic conditions (45%). The efficiency of photoluminescence (PL) was also best preserved under these conditions, although it was 30 times less than the PL of hydrophobic QDs. Then, all three kinds of hydrophilic QDs were dispersed in solutions with a wide range of pH (2–12) and investigated by absorbance and PL measurements. The results show that QDs subjected to a ligand exchange procedure are characterized by intensive PL at the selected pH values, which correspond to pKa of the ligand. This phenomenon is independent of the pH at which the ligand exchange procedure is conducted. Moreover, it was found that the PL intensity is preserved during the experiment for QDs functionalized under neutral conditions, whereas it decreases for acidic and increases for alkaline conditions. [ABSTRACT FROM AUTHOR]

Abstract: An useful electrochemical sensing approach was developed for epinephrine (EP) detection based on graphene quantum dots (GQDs) and laccase modified glassy carbon electrodes (GC). The miniature GC biosensor was designed and constructed via the immobilization of laccase in an electroactive layer of the electrode coated with carbon nanoparticles. This sensing arrangement utilized the catalytic oxidation of EP to epinephrine quinone. The detection process was based on the oxidation of catecholamine in the presence of the enzyme – laccase. With the optimized conditions, the analytical performance demonstrated a high degree of sensitivity −2.9 μA mM−1 cm−2, selectivity in a broad linear range (1–120×10−6 M) with detection limit of 83 nM. Moreover, the method was successfully applied for EP determination in labeled pharmacological samples. [ABSTRACT FROM AUTHOR]

In the paper, the development and performance of an optical sensor for detection of neurotransmitters (dopamine) is presented. The concentration of dopamine is measured basing on fluorescence quenching of graphene quantum dots. In the sensor, the dopamine molecules coat the graphene quantum dots surface - in result, the quenching of fluorescence occurs due to the Förster resonance energy transfer. The changes in fluorescence correspond to specific concentrations of the neurotransmitter in tested samples, so it is possible to accurately determine the concentration of dopamine in the sample. [ABSTRACT FROM AUTHOR]

Fundamentals of quantum dots (QDs) sensing phenomena show the predominance of these fluorophores over standard organic dyes, mainly because of their unique optical properties such as sharp and tunable emission spectra, high emission quantum yield and broad absorption. Moreover, they also indicate no photo bleaching and can be also grown as no blinking emitters. Due to these properties, QDs may be used e.g., for multiplex testing of the analyte by simultaneously detecting multiple or very weak signals. Physico-chemical mechanisms used for analyte detection, like analyte stimulated QDs aggregation, nonradiative Förster resonance energy transfer (FRET) exhibit a number of QDs, which can be applied in sensors. Quantum dots-based sensors find use in the detection of ions, organic compounds (e.g., proteins, sugars, volatile substances) as well as bacteria and viruses. [ABSTRACT FROM AUTHOR]

A convenient fluorescence sensing strategy for dopamine (DA) detection was developed based on polydopamine (poly(DA)) formed on the surface of graphene quantum dots (GQDs). The prepared GQDs were highly luminescent due to the planar structure in aromatic molecules. The ceramic-based miniature biosensor was designed and constructed through the immobilization of laccase in an electrochemically synthesized polymer − poly[dithienotetraphenylsilane] based on low temperature co-fired ceramics technology (LTCC). This sensing system utilized the catalytic oxidation of DA to dopamine- o -quinone (DOQ), and then to poly(DA) (in alkaline conditions), which can selectively quench the strong luminescence of GQDs owing to Förster resonance energy transfer (FRET). The detection process was based on substarte oxidation in the presence of the enzyme − laccase. In optimized conditions, the analytical performance illustrated high sensitivity, selectivity in a broad linear range with detection limit of 80 nM. Moreover, the method was successfully applied to test labeled pharmacological samples for DA. [ABSTRACT FROM AUTHOR]