Photoelectrochemical quenching-recovery biosensor based on NSCQDs/Fe2O3@Bi2S3 for the detection of trypsin

BACKGROUND

The content of trypsin will change when pancreatic diseases occur, therefore developing a high-performance method for trypsin detection is of great significance for guiding patients on medication plans and improving their prognosis. Photoelectrochemical (PEC) analysis techniques have emerged as a solution to apply for bioassays.

RESULTS

Herein, the Fe2O3@Bi2S3 and Nitrogen and sulfur co-doped carbon quantum dots (NSCQDs) were successfully synthesized by a hydrothermal method. Subsequently, NSCQDs/Fe2O3@Bi2S3 with a photocurrent amplification effect covered on fluorine-doped tin oxide (FTO) electrode as the substrate material and apoferritin (APO) as a bio-recognition element to quench the photocurrent of the substrate material which can be excited with light. Due to the decomposition specifically between APO and trypsin, the photocurrent response increased. The linear range for trypsin detection showed satisfied results from 2 to 1000 ng mL-1 under optimal conditions, with a detection limit of 0.42 ng mL-1 and a recovery rate of 97.41 %-103.02 %, enabling efficient quantitative analysis of trypsin.

SIGNIFICANCE

In this experiment, a PEC biosensor with simple operation, low detection limit, excellent selectivity and strong stability was successfully prepared, enabling quantitative analysis of trypsin in human serum samples through the quenching-recovery mechanism. It holds great significance for diagnosis and serves as a practical method for the detection of trypsin in the future.

Ultrasensitive Determination of Trypsin in Human Urine Based on Amplified Fluorescence Response

The determination of trypsin activity in human urine is important for evaluating pancreatic disease. We designed an effective fluorescence sensing strategy based on a self-assembled amphiphilic pyrene/protamine complex system that provides an amplified fluorescence response for highly sensitive and selective detection of trypsin. In aqueous solution, the functionalized pyrene formed fluorescent, π-extended aggregates inside micelles, which were effectively quenched by protamine (a trypsin substrate). However, this quenched fluorescence was very sensitively recovered by the trypsin's enzymatic reaction, and this was attributed to a marked reduction in enhanced exciton migration caused by protamine in π-delocalized pyrene aggregates. The devised sensing platform was successfully utilized to selectively and sensitively detect trypsin at very low concentrations (0.03-0.5 μg mL^-1) in non-pretreated human urine and to screen for trypsin inhibitors at concentrations of 0.1-5.0 μg mL^-1.

Ultrasensitive ratiometric fluorescent probes for Hg(ii) and trypsin activity based on carbon dots and metalloporphyrin via a target recycling amplification strategy

A ultrasensitive ratiometric fluorescent probe was developed for Hg(ii) and trypsin based on CDs and TPPS via a target recycling amplification strategy. The detection limits of Hg2+ and trypsin were 0.086 nM and 0.013 ng mL−1.

Nitrogen-doped carbon quantum dots fabricated from cellulolytic enzyme lignin and its application to the determination of cytochrome c and trypsin

A sensitive and effective strategy for the detection of cytochrome c (Cyt c) and trypsin was developed using biomass nitrogen-doped carbon quantum dots (N-CQDs) as the fluorescence probe. N-CQDs were synthesized through a one-pot hydrothermal method by utilizing cellulolytic enzyme lignin as the carbon source and ammonia as the solvent and nitrogen source. The obtained N-CQDs had good water solubility and stable optical properties. The introduction of nitrogen increased fluorescence quantum yield (QY) to 8.23%, which was almost four times as high as that before nitrogen doping. The N-CQDs were fabricated as a label-free biosensor to detect Cyt c and trypsin. The fluorescence of N-CQDs was quenched with positively charged Cyt c due to electrostatic induction aggregation and static quenching. However, Cyt c tended to be hydrolyzed into small peptides in the presence of trypsin, which caused fluorescence recovery of the N-CQDs/Cyt c complex. A wide linear response range was achieved for Cyt c within 1-50 μM and the developed N-CQDs/Cyt c complex displayed a linear response for trypsin within 0.09-5.4 U/mL. The detection limits were 0.29 μM for Cyt c and 0.013 U/mL for trypsin, respectively. Furthermore, this assay had been applied to Cyt c and trypsin detection in serum samples with the recoveries in the range of 94.6-98.5% and 95.5-102.0%, respectively. The established method was sensitive, selective, easy to operate, and low cost, which proved its potential application in clinical diagnosis. The synthesis and fluorescence mechanism of N-CQDs and the strategy for Cyt c and trypsin detection.

Label-free analytical performances of a peptide-based QCM biosensor for trypsin

A label-free biosensor was fabricated for the detection of trypsin by using a peptide-functionalized quartz crystal microbalance gold electrode. The synthetized peptide chains were immobilized tightly on the QCM electrode via a self-assembly method, which formed a thin and approximate rigid layer of peptides. The detection signal was achieved by calculating the mass changes on the QCM electrode because the peptide chains could be specifically cleaved in the carboxyl terminuses of arginine and lysine by trypsin. When gold nanoparticles were coupled to the peptide chains, the sensing signal would be amplified 10.9 times. Furthermore, the sensor interface shows a lower resonance resistance change when the peptide chain is immobilized horizontally. Independent detections in parallel on different electrodes have a wide linear range. Under the optimum conditions, the signal-amplified biosensor allowed the measurement of trypsin over the range of 0-750 ng mL-1 with a detection limit of 8.6 ng mL-1. Moreover, for screening the inhibitor of trypsin, the IC50 values were obtained to be 1.85 μg mL-1 for benzamidine hydrochloride and 20.5 ng mL-1 for the inhibitor from soybean.

A fluorometric sensing method for sensitive detection of trypsin and its inhibitor based on gold nanoclusters and gold nanoparticles

In this work, a facile, label-free, and sensitive fluorometric strategy for detection of trypsin and its inhibitor was established on the basis of the fluorescence resonance energy transfer (FRET) between mercaptoundecanoic acid functionalized gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs) via protamine as a bridge. Protamine can trigger the aggregation of AuNPs and link AuNCs with aggregated AuNPs through electrostatic interaction. Compared with monodisperse AuNPs, the UV-vis absorption band of aggregated AuNPs overlapped considerably with the emission spectrum of AuNCs. Thus, the fluorescence of AuNCs was obviously quenched by the aggregated AuNPs through FRET. In the presence of trypsin, protamine was hydrolyzed into small fragments, leading to the deaggregation of AuNPs and breaking of the short distance between AuNPs and AuNCs, so the FRET process was inhibited, and the fluorescence of AuNCs was recovered. The increase in the fluorescence intensity of AuNCs was directly related to the amount of trypsin. Hence trypsin can be determined on the basis of the variation of fluorescence intensity, with a linear range of 5-5000 ng mL-1 and a detection limit of 1.9 ng mL-1. In addition, this system was used for the detection of trypsin inhibitor by application of the inhibitor isolated from soybean as a model. The sensing method was applied for trypsin detection in human urine and commercial multienzyme tablet samples with satisfactory results. Graphical abstract ᅟ.

Ultrasensitive detection of trypsin activity and inhibitor screening based on the electron transfer between phosphorescence copper nanocluster and cytochrome c

Trypsin, as one of important proteases, is specific for catalyzing the hydrolysis of peptide and ester bonds containing lysine and arginine residues at the C-terminus. The level of trypsin in biological fluids can serve as a reliable and specific diagnostic biomarker for pancreatic function and its pathological changes. Herein, we demonstrate the application of phosphorescent Cu NCs for trypsin detection for the first time depending on the electron transfer between Cu NCs and cyt c. Cyt c and Cu NCs were selected as the quencher and the fluorophore, respectively. Cu NCs could bind to the positively charged cyt c through electrostatic and hydrophobic interactions, and the phosphorescence of Cu NCs was efficiently quenched by the metal-containing heme of cyt c. In the presence of trypsin, cyt c was digested, thus phosphorescence of Cu NCs remained. Therefore, a new and continuous phosphorescence assay for the detection of trypsin activity and its inhibitor screening was established. The plot of relative fluorescence versus trypsin concentration obtains a good linear detection range from 0 to 20 ng/mL (R² = 0.9657), and a detection limit of 2 ng/mL, which is much lower than 20 ng/mL of the sensor in buffer solution because of urine amplifying the phosphorescence signal of Cu NCs based on the FRET strategy. This assay still has been successfully applied to trypsin inhibitor screening, demonstrating its potential application in drug discovery.

A real-time fluorescence assay for protease activity and inhibitor screening based on the aggregation-caused quenching of a perylene probe

We have established a real-time and label-free fluorescence turn-on strategy for protease activity detection and inhibitor screening via peptide-induced aggregation-caused quenching of a perylene probe. Because of electrostatic interactions and high hydrophilicity, poly-l-glutamic acid sodium salt (PGA; a negatively charged peptide) could induce aggregation of a positively charged perylene probe (probe 1) and the monomer fluorescence of probe 1 was effectively quenched. After a protease was added, PGA was enzymatically hydrolyzed into small fragments and probe 1 disaggregated. The fluorescence recovery of probe 1 was found to be proportional to the concentration of protease in the range from 0 to 1 mU/ml. The detection limit was down to 0.1 mU/ml. In the presence of a protease inhibitor, protease activity was inhibited and fluorescence recovery reduced. Moreover, we demonstrated the potential application of our method in a complex mixture sample including 1% human serum. Our method is simple, fast and cost effective.

A sensitive and label-free trypsin colorimetric sensor with cytochrome c as a substrate

The development of simple and sensitive methods for protease sensing plays important roles in clinical diagnostics and drug development. Here a simple, rapid, label-free, and sensitive trypsin colorimetric sensor was developed by employing cytochrome c (cyt c) as an enzyme substrate and 3,3´,5,5´-tetramethylbenzidine (TMB) as a chromogenic reagent. It was found that cyt c hardly catalyzes H2O2-mediated TMB oxidation to produce a blue solution. But the hydrolysate of cyt c by trypsin displays an intense catalytic effect on the aforementioned reaction, resulting in the formation of a blue solution immediately. The detection process allows visually perceiving as low as 50 ng/mL trypsin with the naked eyes. With the aid of a spectrophotometer, the absorbance at 652 nm was proportional to the concentration of trypsin in the range from 5.0 ng/mL to 2.0 μg/mL with a detection limit of 4.5 ng/mL. The sensor showed better precision with relative standard deviation of 2.5% and 1.7% for eleven repetitive measurements of 50.0 ng/mL and 1.0 μg/mL trypsin solution, respectively. The procedure has been successfully applied to the determination of trypsin in human urines and for inhibitor screening, demonstrating its potential application in clinic diagnosis and drug development.

A sensitive assay for trypsin using poly(thymine)-templated copper nanoparticles as fluorescent probes

A new, simple and sensitive fluorescence strategy was developed for the trypsin assay based on copper nanoparticles (CuNPs) and its different fluorescence response toward trypsin-catalyzed hydrolysis of cytochrome c (Cyt c). Polythymine (poly T)-templated CuNPs served as effective fluorescent probes. Cyt c is well-known to act as a quencher. However, herein, a low concentration of Cyt c was designed specially to act as the substrate of trypsin to avoid the quenching effects by electron transfer from Cyt c to CuNPs. In the presence of trypsin, Cyt c hydrolyzes to small peptides, releasing free cysteine residues. Nonfluorescent coordination complexes were formed upon exposure to free cysteine residues by a metal-ligand bond between Cu atoms and sulfur atoms, leading to a decreased fluorescence response to CuNPs. This novel method for the quantitative determination of trypsin has a linear detection range from 0.25 μg mL(-1) to 1000 μg mL(-1) and a relatively low detection limit of 42 ng mL(-1). To the best of our knowledge, this is the first application of the trypsin-catalyzed hydrolysis reaction of Cyt c to produce quenching effect in bioanalysis, which provided a novel approach for the biochemical sensing strategy.

Gold nanoclusters-based chemiluminescence resonance energy transfer method for sensitive and label-free detection of trypsin

A chemiluminescence resonance energy transfer (CRET) platform was developed for sensitive and label-free detection of protease by using trypsin as a model analyte. In this CRET platform, bis(2,4,6-trichlorophenyl)oxalate-hydrogen peroxide chemiluminescence (CL) reaction was utilized as an energy donor and bovine serum albumin (BSA)-stabilized gold nanoclusters (Au NCs) as an energy acceptor. The BSA-stabilized Au NCs triggered the CRET phenomenon by accepting the energy from TCPO-H2O2 CL reaction, thus producing intense CL. In the presence of trypsin, the protein template of BSA-stabilized Au NCs was digested, which frustrated the energy transfer efficiency between the CL donor and the BSA-stabilized Au NCs, leading to a significant decrease in the CL signal. The decreased CL signal was proportional to the logarithm of trypsin concentration in the range of 0.01-50.0µg mL(-1). The detection limit for trypsin was 9ng mL(-)(1) and the relative standard deviations were lesser than 3% (n=11). This Au NCs-based CRET platform was successfully applied to the determination of trypsin in human urine samples, demonstrating its potential application in clinical diagnosis.

Chemiluminescence detection of a protein through the aptamer-controlled catalysis of a porphyrin probe

Sensitive and selective protein detection based on the aptamer-controlled noncovalent porphyrin probe self-assembly is reported for the first time. Vascular endothelial growth factor (VEGF) is a predominant biomarker in cancer angiogenesis. In this work, a positively charged porphyrin probe, manganese(III) meso-tetrakis(N-methylpyridinum-4-yl)porphyrin (Mn-PyP), was prepared. Using it as a catalyst, a label-free chemiluminescence (CL) turn-on approach for sensitive VEGF detection is developed. Mn-PyP could catalyze the luminol CL reaction. The VEGF aptamer could induce aggregation of Mn-PyP. As a result, the Mn-PyP-catalyzed CL reaction is efficiently suppressed. Upon the addition of VEGF, the specific binding of VEGF to the aptamer weakens the interactions between the aptamer and Mn-PyP. The Mn-PyP monomers are released, and a turn-on CL signal is thus detected. Our method is quite sensitive; 50 pM of VEGF could be easily detected. It is also very selective against other proteins. Our assay provides an aptamer-based efficient way for protein quantification.

A label-free fluorescence assay for trypsin based on the electron transfer between oligonucleotide-stabilized Ag nanoclusters and cytochrome c

A label-free fluorescent assay for the detection of trypsin by using oligonucleotide-templated silver nanoclusters (Ag NCs) and cytochrome c (Cyt c) has been demonstrated. When negatively charged Ag NCs and positively charged Cyt c are mixed, they tend to form a hybrid complex, and then lead the fluorescence of Ag NCs to be quenched significantly due to electron transfer between Ag NCs and the heme cofactor of Cyt c. In the presence of trypsin, it catalyzes the hydrolytic cleavage of Cyt c to small peptide fragments, and releases the heme moiety from the Ag NCs/Cyt c complex; the quenched fluorescence restores therewith. By virtue of this specific response, the fluorescent biosensor has a linear range of from 0.7 to 4 μg mL(-1) and from 9 to 120 μg mL(-1) with a detection limit of 58.7 ng mL(-1). Aside from the easy manufacture aspect, our method also possesses a high signal-to-background ratio (~11), excellent selectivity and good biocompatibility, which makes it a promising bioanalysis for a trypsin activity assay.

A continuous-flow mass biosensor for the real-time dynamic analysis of protease inhibition

A flow injection analysis–quartz crystal microbalance (FIA–QCM) biosensor system was introduced for probing the dynamic interactions during protease inhibition.