A signal-switchable fluorescent probe for detection of HPO4 2- based on 5,10,15,20-(4-sulphonatophenyl)porphyrin (TPPS4 ).

In this study, 5,10,15,20-(4-sulphonatophenyl)porphyrin (TPPS4 ) was selected as a fluorescent probe due to its excellent characteristics including high quantum yield, good water solubility, and exceptional biocompatibility. With an excitation wavelength set at 515 nm, the optimal fluorescence emission wavelength for TPPS4 was measured at 642 nm. At this moment, the fluorescence signal of TPPS4 pink solution was in the 'ON' state. The fluorescence intensity of TPPS4 was quenched when ascorbic acid (AA) was introduced, which was due to the electron transfer quenching effect between AA and TPPS4 . The colour of the corresponding solution changed from pink to green, and the fluorescence signal was in the 'OFF' state. When HPO4 2- was further introduced into the TPPS4 -AA system, the quenched fluorescence intensity of TPPS4 was recovered due to the unique interaction between HPO4 2- and AA. At this time, the colour of the corresponding solution changed from green to red, and the fluorescence signal was in the 'ON' state. Therefore, an 'ON-OFF-ON' signal-switchable fluorescent probe was constructed based on TPPS4 to detect HPO4 2- . The results showed that the linear range of HPO4 2- was 4.0 × 10-9 to 1.7 × 10-6  M, and the detection limit was 1.3 × 10-9  M (S/N = 3). The sensing system exhibited high accuracy and sensitivity, and it could be used successfully to detect HPO4 2- in real samples.

Simultaneous fluorescence sensing of vitamin B2 and sulfur ions based on fluorescent copper nanoparticles.

In this study, the F-CuNPs were synthesized by a modified liquid-phase chemical reduction method. Throughout the preparation process, anhydrous copper sulfate was used as the copper source, and ascorbic acid in the NaOH solution served as the reducing and protective agent. Förster resonance energy transfer (FRET) may exist between F-CuNPs and vitamin B2 due to the large spectral overlap between the fluorescence emission spectra of F-CuNPs and the UV-vis absorption spectra of vitamin B2. Therefore, the detection of vitamin B2 was designed based on a FRET system between F-CuNPs and vitamin B2. With S2- into the F-CuNPs&VB2 system, the fluorescence intensity of vitamin B2 was quenched, while the fluorescence intensity of F-CuNPs was almost unchanged. There may be a specific reaction between S2- and vitamin B2. Therefore, the research system can be further used to detect S2- based on ratiometric fluorescent probe. The research findings show that the linear range of vitamin B2 was 0.51 nM-34.64 nM with a detection limit of 0.25 nM (S/N = 3), the linear range of S2- was 0.64 µM-60.00 µM with a detection limit of 0.32 µM (S/N = 3). Furthermore, the simultaneous fluorescent sensing system has high sensitivity and selectivity. Therefore, this system was designed and successfully used to detect the content of vitamin B2 and S2- in actual samples to find a new effective method to detect analytes.

Novel "on-off" fluorescence sensing for rapid and accurate determination of Cr3+ based on g-CNQDs.

Cr3+ is one of the most essential trace elements in living organisms and plays a vital role in human metabolism. However, both deficiency and excess intake of Cr3+ can be harmful to the human body. Therefore, the quantitative determination of Cr3+ is of great significance in the field of life science. Based on this, in this study, a g-CNQDs@p-acetaminophenol fluorescence sensing system was developed for the quantitative detection of Cr3+ in actual complex samples. G-CNQDs were synthesized with sodium citrate and urea as precursors. The fluorescence signal was enhanced by the synergistic effect between p-acetaminophenol (APAP) and g-CNQDs. The fluorescence quenching phenomenon can be produced when Cr3+ is introduced into the fluorescence-enhanced g-CNQDs@p-acetaminophenol system. An "on-off" fluorescence sensing system was constructed based on g-CNQDs@p-acetaminophenol for the quantitative detection of Cr3+. The experimental data showed a wide linear region in the concentration range of 0.64-63.0 µM, and the detection limit was as low as 0.23 µM. The construction of the sensor system broadens the research field for the practical application of Cr3+.

An innovative study on the "on-off-on" detection of sulfur ions based on a TSPP-riboflavin fluorescent probe.

In this paper, 5,10,15,20-(4-sulphonatophenyl) porphyrin (TSPP) was synthesized by a facile route and used as a fluorescent probe to construct a sensor system based on the high water solubility and high quantum yield. It was found that when riboflavin (RF) was introduced into the TSPP solution, the fluorescence intensity of TSPP decreased for the peaks at 645 nm and 700 nm based on the principle of the electrostatic attractions and hydrophobic interactions between TSPP and riboflavin. When the fluorescence emission peak of riboflavin appeared at 550 nm, the fluorescence sensor system changed from the "on" state to the "off" state. When sulfur ions (S2-) were further introduced into the TSPP-riboflavin system, the fluorescence intensity of riboflavin was further decreased based on the specific reaction between S2- and riboflavin. However, the fluorescence signal of TSPP was restored and the fluorescence sensing system changed from the "off" state to the "on" state. Therefore, TSPP was used as a fluorescent probe to construct an "on-off-on" fluorescent sensing system, the linear range of S2- detected by this system is 5.0 × 10-9 to 3.6 × 10-5 M, and the detection limit (LOD) is 1.1 × 10-9 M. The sensing system has higher accuracy and sensitivity, and it can be successfully used in the sensing of S2- in real samples.