High sensitive trypsin activity evaluation applying a nanostructured QCM-sensor

Purification and partial physical-chemical characterization of a new bovine trypsin proteoform (zeta-trypsin)

Recent advancements in enzyme research have unveiled a new proteoform of bovine trypsin, expanding our understanding of this well-characterized enzyme. While generally similar to other trypsins, this novel proteoform comprises three polypeptide chains, marking a significant difference in activity, kinetic properties, and conformational stability. Compared with the already known bovine trypsin proteoforms, the results showed a lower: activity, kcat and kcat.KM-1 and protein 'foldedness' ratio for the new proteoform. Molecular autolysis, a common feature in trypsin and chymotrypsin, has been explored through comparative physical chemistry properties with other proteoforms. This new proteoform of trypsin not only enriches the existing enzyme repertoire but also promises to shed light on the intricate physiological pathway for enzyme inactivation. Our results suggest that the new trypsin proteoform is one of the likely final pathways for enzyme inactivation in a physiological environment. This discovery opens up new avenues for further research into the functional implications of this new trypsin proteoform.

A Surface Acoustic Wave (SAW)-Based Lab-on-Chip for the Detection of Active α-Glycosidase

Enzyme detection in liquid samples is a complex laboratory procedure, based on assays that are generally time- and cost-consuming, and require specialized personnel. Surface acoustic wave sensors can be used for this application, overcoming the cited limitations. To give our contribution, in this work we present the bottom-up development of a surface acoustic wave biosensor to detect active α-glycosidase in aqueous solutions. Our device, optimized to work at an ultra-high frequency (around 740 MHz), is functionalized with a newly synthesized probe 7-mercapto-1-eptyl-D-maltoside, bringing one maltoside terminal moiety. The probe is designed ad hoc for this application and tested in-cuvette to analyze the enzymatic conversion kinetics at different times, temperatures and enzyme concentrations. Preliminary data are used to optimize the detection protocol with the SAW device. In around 60 min, the SAW device is able to detect the enzymatic conversion of the maltoside unit into glucose in the presence of the active enzyme. We obtained successful α-glycosidase detection in the concentration range 0.15-150 U/mL, with an increasing signal in the range up to 15 U/mL. We also checked the sensor performance in the presence of an enzyme inhibitor as a control test, with a signal decrease of 80% in the presence of the inhibitor. The results demonstrate the synergic effect of our SAW Lab-on-a-Chip and probe design as a valid alternative to conventional laboratory tests.

A Label-Free Fluorescence Aptasensor Based on G-Quadruplex/Thioflavin T Complex for the Detection of Trypsin

A novel, label-free fluorescent assay has been developed for the detection of trypsin by using thioflavin T as a fluorescent probe. A specific DNA aptamer can be combined by adding cytochrome c. Trypsin hydrolyzes the cytochrome c into small peptide fragments, exposing the G-quadruplex part of DNA aptamer, which has a high affinity for thioflavin T, which then enhances the fluorescence intensity. In the absence of trypsin, the fluorescence intensity was inhibited as the combination of cytochrome c and the DNA aptamer impeded thioflavin T’s binding. Thus, the fluorescent biosensor showed a linear relationship from 0.2 to 60 μg/mL with a detection limit of 0.2 μg/mL. Furthermore, the proposed method was also successfully employed for determining trypsin in biological samples. This method is simple, rapid, cheap, and selective and possesses great potential for the detection of trypsin in bioanalytical and biological samples and medical diagnoses.

Analysis of trypsin activity at β-casein layers formed on hydrophobic surfaces using a multiharmonic acoustic method

Proteolysis of milk proteins, such as caseins, caused by milk proteases, can change the organoleptic and nutritional characteristics of milk, and therefore it is essential to monitor this enzymatic activity. We used trypsin as a model protease because of its role as a biomarker for pancreatitis. The aim of this work was to demonstrate the detection of proteolysis of β-casein by trypsin using a multiharmonic quartz crystal microbalance (QCM) biosensor. The β-casein layer was deposited from a 0.1 mg mL^-1 solution on a hydrophobic surface consisting of a self-assembled monolayer of 1-dodecanethiol on the gold electrode of the QCM. The addition of an increasing concentration of trypsin leads to the removal of the casein layer due to proteolysis, and correlates with an increase in the resonant frequency of the QCM. We investigated the effect of trypsin concentrations (0.3-20 nM) on the kinetics of the proteolysis of β-casein and demonstrated that the frequency increase is proportional to the protease concentration. Consequently, an inverse Michaelis-Menten model was used to estimate the Michaelis-Menten constant (K_M = 0.38 ± 0.02 nM) and the limit of detection (LOD = 0.16 ± 0.02 nM). The thickness, mass and viscoelastic properties of the protein adlayer after its formation and following the proteolytic cleavage were evaluated by means of multi-harmonic analysis. We found that β-casein is preferably adsorbed on the hydrophobic surfaces as an asymmetrical double layer, of which the innermost layer was found to be denser and thinner (about 2.37 nm) and the outermost layer was found to be less tightly bound and thicker (about 3.5 nm).

A ratiometric fluorescence strategy based on polyethyleneimine surface-modified carbon dots and Eosin Y for the ultrasensitive determination of protamine and trypsin

A ratiometric fluorescent nanoprobe for protamine and trypsin detection with excellent biocompatibility and high sensitivity was successfully constructed based on CDs-PEI and Eosin Y.

Coenzyme-Mediated Electro-RAFT Polymerization for Amplified Electrochemical Interrogation of Trypsin Activity

Trypsin is a key proteolytic enzyme in the digestive system and its abnormal levels are indicative of some pancreatic diseases. Taking advantage of the coenzyme-mediated electrografting of ferrocenyl polymers as a novel strategy for signal amplification, herein, a signal-on cleavage-based electrochemical biosensor is reported for the highly selective interrogation of trypsin activity at ultralow levels. The construction of the trypsin biosensor involves (i) the immobilization of peptide substrates (without free carboxyl groups) via the N-terminus, (ii) the tryptic cleavage of peptide substrates, (iii) the site-specific labeling of the reversible addition-fragmentation chain transfer (RAFT) agents, and (iv) the grafting of ferrocenyl polymers through the electro-RAFT (eRAFT) polymerization, which is mediated by potentiostatic reduction of nicotinamide adenine dinucleotide (NAD⁺) coenzymes. Through the NAD⁺-mediated eRAFT (NAD⁺-eRAFT) polymerization of ferrocenylmethyl methacrylate (FcMMA), the presence of a few tryptic cleavage events can eventually result in the recruitment of a considerable amount of ferrocene redox tags. Obviously, the NAD⁺-eRAFT polymerization is low-cost and easy to operate as a highly efficient strategy for signal amplification. As expected, the as-constructed biosensor is highly selective and sensitive toward the signal-on interrogation of trypsin activity. Under optimal conditions, the detection limit can be as low as 18.2 μU/mL (∼72.8 pg/mL). The results also demonstrate that the as-constructed electrochemical trypsin biosensor is applicable to inhibitor screening and the interrogation of enzyme activity in the presence of complex sample matrices. Moreover, it is low-cost, less susceptible to false-positive results, and relatively easy to fabricate, thus holding great potential in diagnostic and therapeutic applications.

Recent applications of QCM-D for the design, synthesis, and characterization of bioactive materials

The clinical translation of bioactive technologies is lacking compared to the number of novel technologies reported in the literature. This is in part due to the difficulties in characterizing bioactive materials to understand and predict their biological response. To progress the field and increase clinical success, more robust analytical techniques must be utilized when investigating novel bioactive materials. The quartz crystal microbalance with dissipation (QCM-D), a label-free sensing instrument based on an acoustic resonator, is used to quantify mass change and viscoelastic parameters from soft materials at the nanoscale, in situ, with precise temporal resolution and operation in both liquid and gaseous environments. The versatility of QCM-D has enhanced the characterization of bioactive polymers and sensing arrays for advanced applications of novel biotechnologies. In this review, we highlight exciting, recent applications of QCM-D for the investigation of bioactive materials. Attention is given to the dynamic mechanical properties of bioactive materials, discerning protein structure on surfaces, probing cell adhesion and cytoskeletal changes, and biosensing applications. We conclude that QCM-D has untapped utility in the pre-clinical investigation of bioactive materials and further utilization can improve the clinical success of novel technologies.

Evaluation of biological activities, structural and conformational properties of bovine beta- and alpha-trypsin isoforms in aqueous-organic media

The study of the biological activity of trypsin isoforms in aqueous-organic media is of great interest to various fields of knowledge and biochemistry applications. Thus enzymatic, structural, and energetic properties of bovine β- and α-trypsin isoforms were compared in aqueous-organic media using 30 mg of each isoform. The results showed that the changes induced on the structure and activity of the same trypsin isoform occur at different concentrations. Better results for activity (ionic strength of 0.11 mol·L^-1, at 37 °C and pH 8.0) were found in 0-40% of ethanolic media in which the activity for β-trypsin was about 60% higher than ɑ-trypsin. The ethanolic system does not cause significant changes in the level of secondary structure but the β-trypsin isoform undergoes a major rearrangement. The use of until 60% (v/v) ethanol showed that β-trypsin presents a denaturation process 17% more cooperative. The organic solvent causes redistribution in the supramolecular arrangement of both isoforms: all concentrations used induced the β-trypsin molecules to rearrange into agglomerates. The ɑ-trypsin rearranges into agglomerates up to 60% (v/v) of ethanol and aggregates at 80% (v/v) of ethanol. Both isoforms keep the enzymatic activity up to 60% (v/v) of ethanol.

Capacitive sensing of triglyceride film reactions: a proof-of-concept demonstration for sensing in simulated duodenal contents with gastrointestinal targeting capsule system

Ingestible capsule systems continue to evolve to overcome drawbacks associated with traditional gastrointestinal (GI) diagnostic and therapeutic processes, such as limitations on which sections of the GI tract can be accessed or the inability to measure local biomarker concentrations. We report an integrated capsule sensing system, utilizing a hybrid packaging scheme coupled with triglyceride film-coated capacitive sensors, for measuring biochemical species present in the duodenum, such as pancreatic lipase and bile acids. The system uses microfabricated capacitive sensors interfaced with a Bluetooth low-energy (BLE)-microcontroller, allowing wireless connectivity to a mobile app. The triglyceride films insulate the sensor surface and react either with 0.01-1 mM lipase via hydrolysis or 0.07-7% w/v bile acids via emulsification in simulated fluids, leading to measurable changes in capacitance. Cross reactivity of the triglyceride films is evaluated in both phosphate buffered saline (PBS) as well as pancreatic trypsin solutions. The film morphology is observed after exposure to each stimulus to better understand how these changes alter the sensor capacitance. The capsule utilizes a 3D-printed package coated with polymers that remain intact in acid solution (mimicking gastric conditions), then dissolve at a duodenum-mimicking neutral pH for triggered opening of the sensing chamber from which we can subsequently detect the presence of pancreatic lipase. This device strategy represents a significant step towards using embedded packaging and triglyceride-based materials to target specific regions of the GI tract and sensing biochemical contents for evaluating gastrointestinal health.

Real-Time Label-Free Kinetics Monitoring of Trypsin-Catalyzed Ester Hydrolysis by a Nanopore Sensor

Trypsin is an important proteolytic enzyme in the digestive system and its activity is a major indicator for evaluating diseases such as chronic pancreatitis. Here, we present a novel label-free method to detect trypsin kinetics using a nanopore technique. A mutant α-hemolysin (M113R)₇ protein nanopore equipped with a polyamine decorated β-cyclodextrin (am₇β-CD) was employed as a sensing platform for the real-time monitoring of the process of trypsin enzymatic cleavage of a substrate Nα-benzoyl-l-arginine ethyl ester (BAEE) at the single molecule level. Significantly, this sensor can exclusively respond to the current modulation caused by the product and prevent interference from the substrate, thus improving detection sensitivity, and it provides a new scheme to detect enzyme activity for cleaving small molecules.

Simple impedimetric sensor for rapid lipase activity quantification

A simple and rapid impedimetric sensor applicable for industrial lipase activity quantification was developed and characterized. It is based on the lipase catalyzed degradation by hydrolysis of a thin nanocomposite substrate sensitive layer deposited on a PCB stick electrode usable as disposable or regenerable. The sensitive layer degradation rate was evaluated by the impedance changes registration along time resulting from its thickness diminution applying a small amplitude AC voltage with a constant frequency. The AC current phase shift variations along the time caused by the impedance changes were registered as s sensor response. The sensor was characterized in terms of linear quantification range, LOD, precision and quantification time. The response time was found to be from 80 to 6 s for the linear concentration range from 0.99x10^-2 to 1.68 U.S.P. U mL^-1 with relative errors from 3.75% to 1.24% respectively and a LOD of 8x10^-3 U.S.P. U mL^-1. Finally, lipase spiked whey samples taken from milk industry were quantified and the results were validated by a titrimetric method revealing a good agreement (relative error less than 4.5%).

Sensitive and selective detection of the highly toxic pesticide carbofuran in vegetable samples by a molecularly imprinted electrochemical sensor with signal enhancement by AuNPs

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity. AuNPs were used as the electron wire for signal amplification, and molecularly imprinted polymer was used as the recognition element. The preparation process of the modified electrode was optimized, and the electrode was characterized using scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry. The results proved that the prepared sensor can selectively detect carbofuran and the AuNPs can increase its sensitivity. The method validation included the systematic evaluation of the linearity, sensitivity, selectivity, reproducibility and stability. The optimized sensor showed a wide linear response to carbofuran in the range from 5.0 × 10⁻⁸ to 4.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.4 × 10⁻⁸ mol L⁻¹. The sensor also exhibited a high selectivity to carbofuran. The real sample analysis for vegetable samples suggested its potential application in the analysis of vegetable samples.

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity.

An ultrasensitive fluorescent nanosensor for trypsin based on upconversion nanoparticles

Trypsin and its inhibitors are relevant to many physiological processes and diseases. In this study, a nanosensor capable of detecting trypsin and its inhibitors was designed based on the fluorescence resonance energy transfer (FRET) between upconversion nanoparticle (UCNP) and gold nanoparticle (AuNP). UCNP and AuNP were linked by a trypsin-sensitive peptide DDDDARC, forming the non-fluorescent UCNP-peptide-AuNP nanosensor. In the presence of trypsin, the peptide was cleaved and the quenched fluorescence was restored; in the presence of trypsin inhibitors, the recovery of the fluorescence was decreased. The nanosensor showed a superb sensitivity and selectivity for trypsin and its inhibitors, with a detection limit of 4.15ngmL^-1 for trypsin. UCNP-peptide-AuNP could eliminate the interference of background fluorescence and avoid the light toxicity, and potentially be used to diagnose trypsin-related diseases or screen trypsin inhibitors.

Smart micro/nanoparticles in stimulus-responsive drug/gene delivery systems

New achievements in the realm of nanoscience and innovative techniques of nanomedicine have moved micro/nanoparticles (MNPs) to the point of becoming actually useful for practical applications in the near future. Various differences between the extracellular and intracellular environments of cancerous and normal cells and the particular characteristics of tumors such as physicochemical properties, neovasculature, elasticity, surface electrical charge, and pH have motivated the design and fabrication of inventive "smart" MNPs for stimulus-responsive controlled drug release. These novel MNPs can be tailored to be responsive to pH variations, redox potential, enzymatic activation, thermal gradients, magnetic fields, light, and ultrasound (US), or can even be responsive to dual or multi-combinations of different stimuli. This unparalleled capability has increased their importance as site-specific controlled drug delivery systems (DDSs) and has encouraged their rapid development in recent years. An in-depth understanding of the underlying mechanisms of these DDS approaches is expected to further contribute to this groundbreaking field of nanomedicine. Smart nanocarriers in the form of MNPs that can be triggered by internal or external stimulus are summarized and discussed in the present review, including pH-sensitive peptides and polymers, redox-responsive micelles and nanogels, thermo- or magnetic-responsive nanoparticles (NPs), mechanical- or electrical-responsive MNPs, light or ultrasound-sensitive particles, and multi-responsive MNPs including dual stimuli-sensitive nanosheets of graphene. This review highlights the recent advances of smart MNPs categorized according to their activation stimulus (physical, chemical, or biological) and looks forward to future pharmaceutical applications.

Highly sensitive, label-free colorimetric assay of trypsin using silver nanoparticles

Herein, we report a simple, sensitive label-free colorimetric assay of trypsin based on silver nanoparticles (AgNPs) aggregation. Generally, a specially designed short peptide chain acts as both the stabilizer of AgNPs and the substrate of trypsin. In the presence of trypsin, the negatively charged part of peptides will be hydrolyzed, leaving the positively charged dipeptide capped on the surface of AgNPs. The electrostatic property alteration then leads to the AgNPs' aggregation in certain salt condition. The solution color may change correspondingly due to the localized surface plasmon resonance, which can be monitored by naked eye and UV-vis spectrophotometry. This novel AgNPs-based colorimetric method for quantitative determination of trypsin has a linear detection range from 2.5 to 200 ng mL(-1) and a rather low detection limit down to 2 ng mL(-1). The determination of trypsin can also be realized in complex biological fluids by the proposed method, demonstrating its great potential utility in the clinical applications in the future.