Yiran Fan,Ziyou Ding,Jia Chen,Chengyu Li,Yingchao Han
Alkaline phosphatase (ALP) is an essential enzyme widely distributed in the human body, and it can hydrolyze pyrophosphate (PPi) under alkaline conditions. Therefore, ALP and PPi activities are associated with many diseases and it is crucial to develop sensitive and selective methods for detecting ALP and PPi. Herein, poly(acrylic acid) (PAA)-Ca2+(Ce3+) nanoclusters fluorescent probe was synthesized aiming to detect PPi and ALP quantitatively. The nanoclusters present monodisperse, and their particle size is 0.9–2.4 nm. The probe exhibits no fluorescence due to electron transfer; whereas it can combine with PPi to yield fluorescence increase, arising from the enhanced electric-dipole transition of Ce3+ under the ligand effect of PPi. Moreover, the probe displays good selectivity to PPi, and the fluorescence changes display a linear relationship with PPi concentration of 3–20 mM (y = 11.29x – 23.47, R2 = 0.994). Furthermore, the probe was mixed with PPi to form PAA-Ca(Ce):PPi nanoparticle (Monodisperse, average size: 1.94 nm) and showed high fluorescence selectivity and responsiveness to ALP due to the ALP hydrolyzing effect and the fluorescence difference between PAA-Ca(Ce):PPi and PAA-Ca(Ce):Pi. Based on the relationship between the fluorescence reduction rate of the probe and the logarithm of ALP concentration (y = 0.0594x – 0.00111, 5–200 U/L, R2 = 0.996), ALP was successfully detected quantitatively, and the detection limit is calculated to be 0.62 U/L. Through this approach, we developed a fluorescence “turn-on” for PPi detection and “turn-off” for ALP detection. This study provides a promising strategy for the diagnosis of diseases related to PPi and ALP.
Qiaozhen Bao,Dan Lin,Yaoran Gao,Lina Wu,Jinhua Fu,Khuslen Galaa,Xinhua Lin,Liqing Lin
Herein we develop a novel “off–on-off” fluorescent nanosensor for the ultra-sensitive detection of protamine and trypsin based on the as-prepared nitrogen and sulphur doped carbon dots (N,S-CDs) and gold nanoparticles (AuNPs). N,S-CDs were treated as fluorophore, while AuNPs were treated as fluorescence absorber. By experimental studies, the fluorescence quenching mechanism of N,S-CDs by AuNPs was inner-filter effect (IFE). Upon addition of protamine to the mixed aqueous of N,S-CDs/AuNPs, the electrostatic interaction and Au-N bond between protamine and AuNPs resulted in AuNPs aggregation, and the quenched fluorescence of N,S-CDs could be recovered. Protamine is rich in arginine and can be specifically hydrolyzed by trypsin, resulting in the deaggregation of AuNPs and further quenching the fluorescence of N,S-CDs. Thus, we can determine the concentration of protamine and trypsin by measuring fluorescence intensity of N,S-CDs. Under the optimized conditions, the fluorescence intensity showed a good linear relationship with protamine concentration of 20–260 ng/mL with the detection limit of 4.7 ng/mL. Meanwhile, quantitative determination of trypsin in a range from 10 to 140 ng/mL with the detection limit of 4.3 ng/mL can be achieved in this fluorescent nanosensor. This fluorescent nanosensor also showed excellent selectivity, and we successfully applied it for the detection of protamine and trypsin in human urine samples. Based on the above findings, we conclude that this novel “off–on-off” fluorescent nanosensor has great potential in clinical diagnosis.
A novel hydrazone-based fluorescent probe ( E )-3-((2-(benzo[ d ]thiazol-2-yl)hydrazono)methyl)-4 H -chromen-4-one ( BTC ) has been rationally designed and synthesized. BTC can subsequently detect Ga 3+ and PPi ions through the absorption and emission off–on-off response with high specificity. Importantly, fluorescent probe BTC can well discriminate Ga 3+ from Al 3+ and In 3+ . The association constant (K) was calculated as 2.06 × 10 4 M −1 , and the limit of detection (LOD) was calculated as 4.88 × 10 -2 μM. Competitive binding studies also illustrated good results of the probe BTC towards Ga 3+ . Job's plot and HRMS results substantiated the 1:1 stoichiometry between BTC and Ga 3+ ion. The interaction binding mode of BTC with Ga 3+ was proposed by HRMS, 1 H NMR spectral titration, UV–vis absorption and fluorescence spectral measurements. The combination of the restraint of the photo-induced electron transfer (PET) process and the chelation enhanced fluorescence (CHEF) process is responsible for the fluorescence enhancement of this probe. The in situ chelated BTC -Ga 3+ could further monitor pyrophosphate ion (PPi) by demetallization process with quenching fluorescence emission. Additionally, the BTC and BTC -Ga 3+ showed good cell permeability and could detect Ga 3+ and PPi ions in onion inner epidermal cells, respectively.
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