Construction of a Turn-off-on Fluorescent System Based On Aggregation Induced Emission of Acetaldehyde Using Carbonized Polymer dots and Tb3.

It was the first time to report the aggregation induced emission (AIE) of acetaldehyde (AA) on the surface of carbonized polymer dots (CPDs) with the auxiliary of Tb3+. Based on the AIE of AA, a turn-off-on fluorescence method was established for AA detection using the porous CPDs-Tb3+ system. The one-pot hydrothermal method was used to obtain CPDs, using milk and polyethyleneimine (PEI) as precursors. In the presence of Tb3+, CPDs aggregated immediately and even forming precipitate, and the fluorescence intensity decreased obviously. AA can effectively embed on the surface of CPDs-Tb3+ due to the porous structure. AA displayed obviously blue fluorescence with excitation wavelength at 370 nm (emission peak at 460 nm), while there was no fluorescence peak when excited at 460 nm. In the CPDs-Tb3+ solution, AA exhibits obvious fluorescence enhancement effect (λex 460 nm, λem 545 nm). And then, AA can be determined by the turn-off-on system based on the linear relationship between fluorescence enhancement and the concentration of AA ranging from 0.04 mM to 42.48 mM. The limit of detection (LOD) was 0.02 mM. The turn-off-on system was successfully applied to determine AA in wine samples. The strategy may be exploited to monitor AA in more drinking or foodstuff samples.

Synthesis of Carbon Dots by Varying Doped Elements and Application in Serine Detection.

Carbon dots (CDs) with different doping elements were successfully synthesized via a simple hydrothermal strategy. 3-amino-4-chlorophenylboronic acid, 3-aminobenzeneboronic acid, aniline, and benzene were used as precursors, respectively. The B/N co-doping CDs (BNCDs) derived from 3-aminobenzeneboronic acid show brightest fluorescence among the CDs products with quantum yield at 0.15. The fluorescence of BNCDs exhibits good photostability and excitation-independent emission behavior. The bright blue emission of BNCDs can be quenched by serine, which is a kind of neutral aliphatic amino acid containing hyroxyl groups with polarity. It is possibly due to the molecular collision between excited state of BNCDs and the ground state of serine. BNCDs can be served as fluorophore probe for the assay of serine based on the efficient quenching effect. The approach for the determination of serine shows a high sensitivity with a detection limit at 0.14 nM, which is lower than those of previous works. Furthermore, the present BNCDs system can be employed to monitor serine in real food and biological samples. The strategy may be a potential way for the application in food safety and biomedicine fields.

A convenient fluorescence sensor of tetracycline based on B, N codoped carbon dots/polymer composite film.

A convenient fluorescence sensor of tetracycline (TC) was constructed based on carbon dots (CDs) and polyvinyl alcohol (PVA) hydrogel film. The immobilization of CDs in PVA carrier can stabilize the fluorescence of CDs by inhibiting the fluorescence quench due to the aggregation of CDs with time. CDs were prepared by a hydrothermal method. CDs showed bright blue fluorescence with the quantum yield of 0.35. The fluorescence of CDs was quenched by TC owing to the inner filter effect. The linear range for TC detection was 0-350 µM and the limit of detection was 0.17 µM. To test conveniently, PVA film was employed to upload CDs. Therefore, a novel sensor for TC was constructed in a visual mode. By comparison with the most of previous works, the present method displayed higher sensitivity and better selectivity. The results suggest that the present sensor has potential applications in the real-time detection of TC in food analysis.

Construction of a ratio fluorescence assay of 5-aminosalicylic acid based on its aggregation induced emission with blue emitting N/P-codoped carbon dots.

Herein, a novel ratio fluorescence method based on N/P-doped carbon dots (NPCDs) for detecting 5-aminosalicylic acid (5-ASA) in mesalazine enteric coated tablets and blood were reported for the first time. NPCDs were successfully prepared through a simple one-step hydrothermal strategy by employing adenosine triphosphate (ATP) and p-toluidine as raw materials. NPCDs exhibit bright blue emissions with excitation/emission peaks at 340/423 nm with moderate quantum yield (20.75%). In addition, 5-ASA has a certain weak fluorescence emission peak at 487 nm. Adding 5-ASA into NPCDs significantly enhanced the fluorescence intensity, which may result from aggregation induced emission (AIE) of 5-ASA on the surface of NPCDs. Therefore, NPCDs only provide self-calibration signals, and their fluorescence remains almost unchanged when co-existing with 5-ASA. Therefore, the ratio of fluorescence at F 487/F 423 was used for detection of 5-ASA. For the fluorometric determination assay, there was a good linear relationship between F 487/F 423 and 5-ASA concentration between 0.50 and 130 µM (R 2 = 0.9979). The detection limit was about 0.13 µM. Therefore, this method is simple, sensitive and low cost, and will be successfully applied to the detection of 5-ASA in drugs.

Dual-emission ratio fluorescence for selective and sensitive detection of ferric ions and ascorbic acid based on one-pot synthesis of glutathione protected gold nanoclusters.

A fluorometric method was proposed for the determination of Fe3+ and ascorbic acid (AA) based on blue and red dual fluorescence emissions of glutathione (GSH) stabilized-gold nanoclusters (AuNCs). AuNCs were synthesized from GSH and tetrachloroauric acid. The fluorescence peaks of AuNCs were at 425 nm and 585 nm, respectively. In the presence of Fe3+, the fluorescence peak at 425 nm can be enhanced and that at 585 nm can be quenched. There is a good linear relationship between the fluorescence intensity ratio for the 425 and 585 nm peaks (F 425/F 585) and the concentration of Fe3+ in the range of 0.75-125 µM. However, when AA was added to the AuNCs-Fe3+ system, the value of F 425/F 585 decreased consistently with the concentration of AA in the range of 0.25-35 µM. The limit of detection for Fe3+ and AA was 227 and 75.8 nM, respectively. The interaction between AuNCs and Fe3+ can induce the ligand-metal charge transfer (LMCT) effect leading to the fluorescence increment at 425 nm, while AA can reduce Fe3+ to Fe2+. The production of Fe2+ can not enhance or quench the fluorescence of AuNCs. By comparison with previous literature, the AuNCs prepared here show two fluorescence peaks without additional fluorescence labels. Furthermore, the method was successfully applied in the determination of Fe3+ and AA in some real samples, such as water, human serum and tablets.

Selective determination of Ag+ in the presence of Cd2+, Hg2+ and Cu2+ based on their different interactions with gold nanoclusters.

In this work, a fluorescence method was developed for selective detection of Ag+ in the presence of Cd2+, Hg2+, and Cu2+ based on gold nanoclusters (AuNCs). That is, bovine serum albumin (BSA) templated AuNCs with double emission peaks were synthesized using BSA as a protective agent. AuNCs with uniform distribution and average size between 2.0 and 2.2 nm were synthesized using a green and simple method, and showed bright orange-red fluorescence under ultraviolet light. AuNCs have two emission peaks at 450 nm and 630 nm with an excitation wavelength of 365 nm. Under alkaline conditions, Cd2+ can combine with the surface sulfhydryl groups of BSA-AuNCs to form Cd-S bonds, which cause AuNCs to aggregate, resulting in an increase in fluorescence intensity at 630 nm. Conversely, due to the d10-d10 metal affinity interaction, the addition of Hg2+ can reduce the fluorescence peak at 630 nm. Ag+ was reduced to Ag0 by gold nuclei in AuNCs, forming a stable hybrid Au@ AgNCs species with blue-shifted and enhanced fluorescence. Finally, the paramagnetic behavior of Cu2+ combined with BSA causes the excited electrons of the gold cluster to lose their energy via ISC, eventually leading to simultaneous quenching of the two emission peaks. The results show that the limit of detection (LOD) of Ag+, Hg2+, Cd2+ and Cu2+ is 1.19 µM, 3.39 µM, 1.83 µM and 5.95 µM, respectively.