A new method to assay protease based on amyloid misfolding: application to prostate cancer diagnosis using a panel of proteases biomarkers

Peptide probes for proteases - innovations and applications for monitoring proteolytic activity

Proteases are excellent biomarkers for a variety of diseases, offer multiple opportunities for diagnostic applications and are valuable targets for therapy. From a chemistry-based perspective this review discusses and critiques the most recent advances in the field of substrate-based probes for the detection and analysis of proteolytic activity both in vitro and in vivo.

Peptide Assembled in a Nano-confined Space as a Molecular Rectifier for the Availability of Ionic Current Modulation

Bioinspired nanochannels have emerged as a powerful tool for bioengineering and biomedical research due to their robust mechanical and controllable chemical properties. Inspired by inward-rectifier potassium (K⁺) channels, herein, the charged peptide assembly has been introduced into a nano-confined space for the modulation of ion current rectification (ICR). Peptide-responsive reaction-triggered sequence changes can contribute to polarity conversion of the surface charge; therefore, ICR reversal (ICRR) is generated. Compared with other responsive elements, natural charged peptides show the merit of controllable charge polarity. By electrochemically monitoring the ICRR as an output signal, one can utilize the peptide assembly-mediated ICRR to construct an ionic sensory platform. In addition, a logic gate has been established to demonstrate the availability of an ionic sensory platform for inhibitor screening. As peptide nanoassemblies may also have various structures and functions due to their diverse properties, the ionic modulation system can provide alternatives for the assay of peptide-associated biotargets with biomedical applications.

Quantitative Detection of Cathepsin B Activity in Neutral pH Buffers Using Gold Microelectrode Arrays: Toward Direct Multiplex Analyses of Extracellular Proteases in Human Serum

Proteases are critical signaling molecules and prognostic biomarkers for many diseases including cancer. There is a strong demand for multiplex bioanalytical techniques that can rapidly detect the activity of extracellular proteases with high sensitivity and specificity. This study demonstrates an activity-based electrochemical biosensor of a 3 × 3 gold microelectrode array for the detection of cathepsin B activity in human serum diluted in a neutral buffer. Proteolysis of ferrocene-labeled peptide substrates functionalized on 200 × 200 μm microelectrodes is measured simultaneously over the nine channels by AC voltammetry. The protease activity is represented by the inverse of the exponential decay time constant (1/τ), which equals to (k_cat/K_M)[CB] based on the Michaelis-Menten model. An enhanced activity of the recombinant human cathepsin B (rhCB) is observed in a low-ionic-strength phosphate buffer at pH = 7.4, giving a very low limit of detection of 8.49 × 10^-4 s^-1 for activity and 57.1 pM for the active rhCB concentration that is comparable to affinity-based enzyme-linked immunosorbent assay (ELISA). The cathepsin B presented in the human serum sample is validated by ELISA, which mainly detects the inactive proenzyme, while the electrochemical biosensor specifically measures the active cathepsin B and shows significantly higher decay rates when rhCB and human serum are activated. Analyses of the kinetic electrochemical measurements with spiked active cathepsin B in human serum provide further assessment of the protease activity in the complex sample. This study lays the foundation to develop the gold microelectrode array into a multiplex biosensor for rapid detection of the activity of extracellular proteases toward cancer diagnosis and treatment assessment.

Multiplexed monitoring of a novel autoantibody diagnostic signature of colorectal cancer using HaloTag technology-based electrochemical immunosensing platform

Background and Purpose: The humoral immune response in cancer patients can be used for early detection of the disease. Autoantibodies raised against tumor-associated antigens (TAAs) are promising clinical biomarkers for reliable cancer diagnosis, prognosis, and therapy monitoring. In this study, an electrochemical disposable multiplexed immunosensing platform able to integrate difficult- and easy-to-express colorectal cancer (CRC) TAAs is reported for the sensitive determination of eight CRC-specific autoantibodies. Methods: The electrochemical immunosensing approach involves the use of magnetic microcarriers (MBs) as solid supports modified with covalently immobilized HaloTag fusion proteins for the selective capture of specific autoantibodies. After magnetic capture of the modified MBs onto screen-printed carbon working electrodes, the amperometric responses measured using the hydroquinone (HQ)/H2O2 system were related to the levels of autoantibodies in plasma. Results: The biosensing platform was applied to the analysis of autoantibodies against 8 TAAs described for the first time in this work in plasma samples from healthy asymptomatic individuals (n=3), and patients with high-risk of developing CRC (n=3), and from patients already diagnosed with colorectal (n=3), lung (n=2) or breast (n=2) cancer. The developed bioplatform demonstrated an improved discrimination between CRC patients and controls (asymptomatic healthy individuals and breast and lung cancer patients) compared to an ELISA-like luminescence test. Conclusions: The proposed methodology uses a just-in-time produced protein in a simpler protocol, with low sample volume, and involves cost-effective instrumentation, which could be used in a high-throughput manner for reliable population screening to facilitate the detection of early CRC patients at affordable cost.

A photoelectrochemical aptasensor based on p-n heterojunction CdS-Cu2O nanorod arrays with enhanced photocurrent for the detection of prostate-specific antigen

A sensitive photoelectrochemical (PEC) aptasensor was constructed for prostate-specific antigen (PSA) detection using an enhanced photocurrent response strategy. The p-n heterostructure CdS-Cu₂O nanorod arrays were prepared on Ti mesh (CdS-Cu₂O NAs/TM) by a simple hydrothermal method and successive ionic-layer adsorption reactions. Compared with the original CdS/TM, the synergistic effect of p-n type CdS-Cu₂O NAs/TM and the internal electric field realizes the effective separation of photoinduced electron-hole pairs and improves the PEC performance. In order to construct the aptasensor, an amino-modified aptamer was immobilized on CdS-Cu₂O NAs/TM to serve as a recognition unit for PSA. After the introduction of PSA, PSA was specifically captured by the aptamer on the PEC aptasensor, which can be oxidized by photogenerated holes to prevent electron-hole recombination and increase photocurrent. Under optimal conditions, the constructed PEC aptasensor has a linear range of 0.1-100 ng·mL^-1 and a detection limit as low as 0.026 ng·mL^-1. The results of aptasensor detection of human serum indicate that it has broad application prospects in biosensors and photoelectrochemical analysis.

A novel signal self-enhancement photoelectrochemical immunosensor without addition of a sacrificial agent in solution based on Ag2S/CuS/α-Fe2O3 n–p–n heterostructure films

A novel signal self-enhancement photoelectrochemical immuno-sensor has been developed based on the curing of sacrificial agent SO₃²⁻ coated-Au NPs sensitizing Ag₂S/CuS/α-Fe₂O₃ n–p–n hetero-structure films for the first time.

Phonon-Assisted Photoluminescence Up-Conversion of Silicon-Vacancy Centers in Diamond

Phonon-assisted anti-Stokes photoluminescence (ASPL) up-conversion lies at the heart of optical refrigeration in solids. The thermal energy contained in the lattice vibrations is taken away by the emitted anti-Stokes photons' ASPL process, resulting in laser cooling of solids. To date, net laser cooling of solids is limited in rare-earth (RE)-doped crystals, glasses, and direct band gap semiconductors. Searching more solid materials with efficient phonon-assisted photoluminescence up-conversion is important to enrich optical refrigeration research. Here, we demonstrate the phonon-assisted PL up-conversion process from the silicon vacancy (SiV) center in diamond for the first time by studying ASPL spectra for the dependence of temperature, laser power, and excitation energy. Although net cooling has not been observed, our results show that net laser cooling might be eventually achieved in diamond by improving the external quantum efficiency to higher than 95%. Our work provides a promising route to investigate the laser cooling effect in diamond.

3-D Electrochemical Impedance Spectroscopy Mapping of Arteries to Detect Metabolically Active but Angiographically Invisible Atherosclerotic Lesions

We designed a novel 6-point electrochemical impedance spectroscopy (EIS) sensor with 15 combinations of permutations for the 3-D mapping and detection of metabolically active atherosclerotic lesions. Two rows of 3 stretchable electrodes circumferentially separated by 120° were mounted on an inflatable balloon for intravascular deployment and endoluminal interrogation. The configuration and 15 permutations of 2-point EIS electrodes allowed for deep arterial penetration via alternating current (AC) to detect varying degrees of lipid burden with distinct impedance profiles (Ω). By virtue of the distinctive impedimetric signature of metabolically active atherosclerotic lesions, a detailed impedance map was acquired, with the 15 EIS permutations uncovering early stages of disease characterized by fatty streak lipid accumulation in the New Zealand White rabbit model of atherosclerosis. Both the equivalent circuit and statistical analyses corroborated the 3-D EIS permutations to detect small, angiographically invisible, lipid-rich lesions, with translational implications for early atherosclerotic disease detection and prevention of acute coronary syndromes or strokes.

Enzymatically Regulated Peptide Pairing and Catalysis for the Bioanalysis of Extracellular Prometastatic Activities of Functionally Linked Enzymes

Diseases such as cancer arise from systematical reconfiguration of interactions of exceedingly large numbers of proteins in cell signaling. The study of such complicated molecular mechanisms requires multiplexed detection of the inter-connected activities of several proteins in a disease-associated context. However, the existing methods are generally not well-equipped for this kind of application. Here a method for analyzing functionally linked protein activities is developed based on enzyme controlled pairing between complementary peptide helix strands, which simultaneously enables elaborate regulation of catalytic activity of the paired peptides. This method has been used to detect three different types of protein modification enzymes that participate in the modification of extracellular matrix and the formation of invasion front in tumour. In detecting breast cancer tissue samples using this method, up-regulated activity can be observed for two of the assessed enzymes, while the third enzyme is found to have a subtle fluctuation of activity. These results may point to the application of this method in evaluating prometastatic activities of proteins in tumour.

Sensitive and low-background electrochemical assay of corin activity via supramolecular recognition and rolling circle amplification

Corin is an important member of type II transmembrane serine proteases that is involved in a variety of cardiovascular and pregnancy-related diseases. Herein, a sensitive and low-background electrochemical method is proposed to assay the activity of corin. In principle, a peptide comprising both the substrate motif of corin and binding site of cucurbit[8]uril (CB[8]) is first designed and immobilized on the electrode surface. Thereafter, via CB[8]-mediated supramolecular recognition, a DNA-primer is recruited, subsequently triggering the rolling circle amplification (RCA) reaction. In this way, a succeeding propagation of DNA strands is achieved on the electrode surface, which would produce remarkable repelling effect against the electrochemical species [Fe(CN)6](3-/4-), and thereby yield a highly minimized background signal. However, in the presence of activated corin, the peptide is specifically recognized and cleaved, breaching the recruitment of DNA primer as well as the RCA reaction, which decreases the repulsion to [Fe(CN)6](3-/4-), leading to a remarkable electrochemical response. As a result, the proposed assay method can sensitively determine the activity of corin with a detection limit of 0.92 pM, and can further be directly used in maternal plasma samples. Therefore, this method may provide a promising tool for pathological research and clinical diagnosis of corin-related diseases.

Peptide-based method for detection of metastatic transformation in primary tumors of breast cancer

Detection of metastatic activity before the onset of the actual metastasis can be a promising method to combat metastasis, the foremost cause of death in cancer. Therefore, in this work, we have developed an assay method for the detection of metastatic tumor cells in primary tumor, by using a protein of the metastatic cell signaling as the biomarker. In this assay, a peptide-based probe targeting the marker protein and a sensitive nanoparticle doped graphene nanolabel are combined to enable the detection of metastatic cells. Consequently, the metastatic cells can be specifically detected and discriminated from primary tumor cells. By applying this assay method to clinical samples of primary tumor, a low amount of metastatic activity can be detected in the tumor sites, which may suggest the activity of local metastatic transformation. So, these results may point to the prospect of using the proposed method for controlling metastatic cancer.

Simple electrochemical sensing of attomolar proteins using fabricated complexes with enhanced surface binding avidity

Target molecules selectively equipped with proximity probes can autonomously cleave substrates on the electrode surface, allowing quantification of proteins at attomolar concentrations with one-step incubation.

Various strategies have been proposed for the detection of disease protein biomarkers; however, most methods are too expensive, cumbersome or limited in sensitivity for clinical use. Here, we report that a fabricated complex can be used as a powerful tool to detect trace proteins in complex samples. In this strategy, a DNA–protein complex that comprises of one target molecule and two or more deoxyribozyme-containing probes can exhibit autonomous cleavage behavior on the surface of the substrate DNA modified electrode. In the meantime, the complex can remove the cleaved DNA fragment from the electrode surface by taking advantage of the proximity effect. The proposed approach allows one-step and highly sensitive detection of a variety of targets based on the changes of the direct electrochemical readout. Moreover, this method may also have considerable advantages over the commonly reported DNA amplification-assisted immunoassays, particularly in terms of assay simplicity and cost, which may hold great potential for application in resource-constrained regions.

Colorimetric assay for protein detection based on "nano-pumpkin" induced aggregation of peptide-decorated gold nanoparticles

Small peptide can be used as an effective biological recognition element and provide an alternative tool for protein detection. However, the development of peptide-based detecting strategy still remains elusive due to the difficulty of signal transduction. Herein, we report a peptide-based colorimetric strategy for the detection of disease biomarker by using vascular endothelial growth factor receptor 1 (Flt-1) as an example. In this strategy, N-terminal aromatic residue-containing peptide modified gold nanoparticles (GNPs) can form bulky aggregate by the introduction of cucurbit[8]uril (CB[8]) that can selectively accommodate two N-terminal aromatic residue of peptides simultaneously regardless of their sequences. However, in the presence of Flt-1, the peptide can specifically bind to the protein molecule and the N-terminal aromatic residue will be occupied, resulting in little aggregation of GNPs. By taking advantage of the highly affinitive peptide and efficiency cross-linking effect of CB[8] to GNPs, colorimetric assay for protein detection can be achieved with a detection limit of 0.2 nM, which is comparable with traditional methods. The feasibility of our method has also been demonstrated in spiked serum sample, indicating potential application in the future.

Peptide network for detection of tissue-remodeling enzyme in the prognosis of hepatocellular carcinoma

In this work, a surface-confined peptide network that can exhibit distinct structural features under protease cleavage and electrochemical treatment is developed as a highly sensitive biosensor for clinical detection of kallikrein 6 (KLK6). KLK6 is a serine protease of the tissue-remodeling process determining the development of hepatocellular carcinoma (HCC). The peptide network, immobilized on the electrode surface by a Au-S bond, loses its integrity upon KLK6 cleavage and is removed from the electrode by electrochemical desorption of thiol groups, while the network without protease cleavage can remain attached by a few intact Au-S bonds. In this manner, distinct conductivity of the electrode surface in the presence/absence of protease can result in a large signal-to-background ratio, enabling KLK6 detection in clinical samples. The detected KLK6 abundance can manifest the correlation between up-regulated KLK6 activity and the progress of HCC. These results suggest a potential future use of this peptide network as a biosensor to provide diagnostic information for better administration of HCC.

A ‘signal on-off’ electrochemical peptide biosensor for matrix metalloproteinase 2 based on target induced cleavage of a peptide

A sensitive ‘signal on–off’ electrochemical peptide biosensor for MMP-2 assay was fabricated based on target induced cleavage of a specific peptide.