A gold nanoparticles colorimetric assay for label-free detection of protein kinase activity based on phosphorylation protection against exopeptidase cleavage

Plasmonic nanoparticle-assisted single-molecule dynamic binding for protein kinase activity digital counting

In this work, we design a new approach for digital counting-based protein kinase activity assay by using plasmonic nanoparticle-assisted single-molecule dynamic binding. This method breaks the concentration-dependent limitation in single-molecule detection and displays good selectivity and sensitivity with a detection limit as low as 0.0001 U mL-1 for the protein kinase A (PKA) assay, which would find broad applications in drug screening and medical investigations.

Zr4+-mediated DNAzyme-driven DNA walker amplification strategy for electrochemical assay of protein kinase a activity and inhibition

Protein kinase A (PKA) can regulate many cellular biological processes by phosphorylation substrate peptide or protein. Sensitive detection of PKA activity is critical for the PKA-related drug discovery and disease diagnosis. A new electrochemical biosensing method was developed for detection of PKA activity based on Zr⁴⁺-mediated DNAzyme-driven DNA walker signal amplification strategy. In this strategy, the special designed substrate peptide and a thiolated methylene blue-labeled hairpin DNA (MB-hpDNA) containing a single ribonucleic acid group (rA) could be anchored on the surface of gold electrode by Au-S bond. In the presence of adenosine triphosphate (ATP) and PKA, substrate peptide was phosphorylated and linked with walker DNA (WD) via the robust phosphate-Zr⁴⁺-phosphate chemistry. The linked WD hybridized with the loop region of MB-hpDNA to form a Mn²⁺-dependent deoxynuclease (DNAzyme), which cleaved the MB-hpDNA into MB-labeled fragment releasing away from electrode surface, resulting in a dramatic decrease of electrochemical signal and providing an electrochemical sensing platform for PKA activity detection. The response signal of the developed biosensor is proportional to the logarithm of PKA concentration in the range of 0.05 U mL^-1 to 100 U mL^-1, with a detection limit of 0.017 U mL^-1 at a signal to noise ratio of 3. Furthermore, the proposed method can also be applied for the evaluation of PKA inhibition and PKA activity assay in cell samples. Therefore, the proposed biosensor shows great promise as a universal tool for diagnostics and drug discovery of PKA-related diseases.

Construction of a phos-tag-directed self-assembled fluorescent magnetobiosensor for the simultaneous detection of multiple protein kinases

Protein kinases play important roles in regulating various cellular processes and may function as potential diagnostic and therapeutic targets for various diseases including cancers. Herein, we construct a phos-tag-directed self-assembled fluorescent magnetobiosensor to simultaneously detect multiple protein kinases with good selectivity and high sensitivity. In the presence of protein kinases (i.e., PKA and Akt1), their substrate peptides (i.e., a FITC-labeled substrate peptide and a Cy5-labeled substrate peptide) are phosphorylated, and are then specifically recognized and captured by a biotinylated phos-tag to generate biotinylated substrate peptides for the assembly of magnetic bead (MB)-peptides-FITC/Cy5 nanostructures. After magnetic separation, the phosphorylated substrate peptides are disassembled from the MB-peptides-FITC/Cy5 nanostructures using deionized water at 80 °C, releasing FITC and Cy5 molecules. The released FITC and Cy5 molecules are detected by steady-state fluorescence measurements, with FITC indicating PKA and Cy5 indicating Akt1. This magnetobiosensor only involves one phos-tag without the requirement of radiolabeling, antibody screening, carboxypeptidase Y (CPY) cleavage, and cumbersome chemical/enzyme reactions. The introduction of magnetic separation can effectively eliminate the interference from complex real samples, generating an extremely low background signal. Moreover, this magnetobiosensor can accurately measure cellular protein kinase activities and screen inhibitors, with great potential for kinase-related biomedical research and therapeutic applications.

A facile fluorescence turn-on biosensor customized for monitoring of protein kinase activity based on carboxylic carbon nanoparticles-peptide complexes

In this study, we present a facile and low-cost approach for detecting protein kinase A (PKA) by assembling a purpose-designed carboxyfluorescein (FAM)-labeled peptide with carboxylic carbon nanoparticles (CNPs). Fluorescence of the FAM-labeled peptide gradually decreases to low background signal as a result of the electron transfer from CNPs to FAM-labeled peptide via the peptide, which acts as a bridge. The reaction in the sensor in the presence of adenosine 5'-triphosphate and PKA phosphorylates the substrate peptide and disrupts the electrostatic repulsive force between the CNPs and the peptide, thus altering the spectroscopic signal of the system. The change in fluorescence signal was directly proportional to the PKA concentration in the range of 0-1.8 U/mL with a detection limit of 0.04 U/mL. These results suggest that PKA activity can be effectively measured using the developed PKA biosensor. Moreover, the fluorescence biosensor was successfully used in the investigation of PKA in spiked human embryonic kidney (HEK) 293 cells lysates, indicating its potential applications in protein kinase-related biochemical fundamental research.

Heterogeneous sensing of post-translational modification enzymes by integrating the advantage of homogeneous analysis

Heterogeneous analysis has great application prospects in the detection of post-translational modification (PTM) enzymes with the advantages of signal enhancement, less sample demand, and high sensitivity and selectivity. Nevertheless, once the substrate was fixed on a solid interface, the steric hindrance might limit the approaching of catalytic center to the substrate, thus reducing the efficiency of PTM. Herein, we suggested that the avidin-modified interface could be used to develop heterogeneous sensing platforms with biotin-labeled substrates as the probes, in which the enzymatic PTM was performed in solution and the heterogeneous assay was conducted on a solid surface. The sensing strategy integrates the advantages but overcomes the defects of both homogeneous and heterogeneous assays. Protein kinase A (PKA) and histone acetyltransferase (HAT) were determined as the examples by using sequence-specific peptide substrates. The signal changes were monitored by HRP-based colorimetric assay and antibody-amplified surface plasmon resonance (SPR). The methods were used for analysis of cell lysates and evaluation of inhibition efficiency with satisfactory results. The strategy can be used for the detection of a variety of biological enzymes and provide a new idea for the design of various heterogeneous biosensors. Thus, this work should be of great significance to the popularization and practical application of biosensors.

Protocols for Characterization of Cdk5 Kinase Activity

Cyclin-dependent kinases (Cdks) are generally known to be involved in controlling the cell cycle, but Cdk5 is a unique member of this protein family for being most active in post-mitotic neurons. Cdk5 is developmentally important in regulating neuronal migration, neurite outgrowth, and axon guidance. Cdk5 is enriched in synaptic membranes and is known to modulate synaptic activity. Postnatally, Cdk5 can also affect neuronal processes such as dopaminergic signaling and pain sensitivity. Dysregulated Cdk5, in contrast, has been linked to neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Despite primarily being implicated in neuronal development and activity, Cdk5 has lately been linked to non-neuronal functions including cancer cell growth, immune responses, and diabetes. Since Cdk5 activity is tightly regulated, a method for measuring its kinase activity is needed to fully understand the precise role of Cdk5 in developmental and disease processes. This article includes methods for detecting Cdk5 kinase activity in cultured cells or tissues, identifying new substrates, and screening for new kinase inhibitors. Furthermore, since Cdk5 shares homology and substrate specificity with Cdk1 and Cdk2, the Cdk5 kinase assay can be used, with modification, to measure the activity of other Cdks as well. © 2021 Wiley Periodicals LLC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Basic Protocol 1: Measuring Cdk5 activity from protein lysates Support Protocol 1: Immunoprecipitation of Cdk5 using Dynabeads Alternate Protocol: Non-radioactive protocols to measure Cdk5 kinase activity Support Protocol 2: Western blot analysis for the detection of Cdk5, p35, and p39 Support Protocol 3: Immunodetection analysis for Cdk5, p35, and p39 Support Protocol 4: Genetically engineered mice (+ and - controls) Basic Protocol 2: Identifying new Cdk5 substrates and kinase inhibitors.

Cationic Polythiophene-based Colorimetric Assay for Probing the Activity of Protein Kinase A

In this work, a novel colorimetric assay based on polythiophene derivative (PMNT) was designed for the detection of protein kinase A (PKA). PKA can catalyze the phosphorylation of peptide, leading to the conformation change of PMNT from random-coil to planar, with the disappearance of absorption peaks above 500 nm and a color change from pink to yellow. The fabricated assay exhibits a wide linear range of 0.05 - 20 U/mL with a detection limit of 0.02 U/mL for PKA activity detection. The proposed protocol has promising prospects for use in clinical diagnosis related to PKA activity.

Label-Free Assay of Protein Kinase A Activity and Inhibition Using a Peptide-Based Electrochemical Sensor

We propose a simple label-free electrochemical biosensor for monitoring protein kinase activity and inhibition using a peptide-modified electrode. The biosensor employs cys-kemptide (CLRRASLG) as a substrate peptide which was immobilized on the surface of a gold electrode via the self-assembly of the thiol terminals in cysteine (C) residues. The interaction between protein kinase A (PKA) and adenosine 5′-triphosphate (ATP) on the cys-kemptide immobilized electrode can cause the transfer of ATP terminal phosphates to the peptide substrates at serine (S) residues, which alters the surface charge of the electrode, thus enabling monitoring of the PKA activity via measuring the interfacial electron transfer resistance with electrochemical impedance spectroscopy. The proposed sensor showed reliable, sensitive, and selective detection of PKA activity with a wide dynamic range of 0.1–100 U/mL and a detection limit of 56 mU/mL. The sensor also exhibited high selectivity, rendering it possible to screen PKA inhibitors. Moreover, the sensor can be employed to evaluate the activity and inhibition of PKA in real samples.

Two-Dimensional Metalloporphyrinic Framework Nanosheet-Based Dual-Mechanism-Driven Ratiometric Electrochemiluminescent Biosensing of Protein Kinase Activity

A dual-mechanism-driven ratiometric electrochemiluminescent (ECL) biosensor was developed for the ultrasensitive detection of protein kinase activity, which was based on a competitive catalytic reaction and resonance energy transfer (RET) by assembling gold nanoparticles (GNPs) on two-dimensional (2D) porphyrinic metal-organic framework (MOF) nanosheets. In this work, an ECL catalytic reaction competing for dissolved O₂ proceeded between 2D copper-based zinc porphyrinic MOF (Cu-TCPP(Zn)) nanosheets and luminol. Meanwhile, the cathodic ECL of singlet oxygen (¹O₂), derived from the electrocatalytic reaction of 2D Cu-TCPP(Zn), would be reduced by the assembled GNPs due to RET, while the anodic emission of luminol could be enhanced by GNPs with excellent electrocatalytic activity. With the detection of protein kinase A (PKA) as an example, this dual-mechanism-driven ECL biosensor exhibited a broad linear range (0.005-5.0 U mL^-1) and a sensitive detection limit (0.0037 U mL^-1). Compared with the traditional single-mechanism-driven sensing strategies, the developed dual-mechanism-driven ratiometric ECL biosensor may provide an effective method for the design of green and ultrasensitive ECL sensors.

Dual-Product Synergistically Enhanced Colorimetric Assay for Sensitive Detection of Lipid Transferase Activity

Lipid transferase-catalyzed protein lipidation plays critical roles in many physiological processes and it has been an increasingly attractive therapeutic target from cancer to neurodegeneration, while sensitive detection of lipid transferase activity in biological samples remains challenging. Here, we presented an AuNP-based colorimetric method with dual-product synergistically enhanced sensitivity for convenient detection of lipid transferase activity. Homo sapiens N-myristoyltransferase 1 (HsNMT1), a key lipid transferase, was selected as the model. Accordingly, positively charged substrate peptides (Pep) of HsNMT1 can induce the aggregation of AuNPs through disrupting their electrostatic repulsion, while the HsNMT1-catalyzed lipid modification generates aggregated lipidated peptides (C14-Pep) and negatively charged HS-CoA, which will eliminate the disruption and stabilize the AuNPs by the formation of Au-S bonds, respectively. Consequently, charge reversal of the biomolecules and the formation of Au-S bonds synergistically contribute to the stability of AuNPs in the presence of HsNMT1. Therefore, the HsNMT1 activity can be visually detected by the naked eye through the color change of the AuNPs originated from the change in their distance-dependent surface plasmon resonance absorptions. Here, the A₅₂₀/A₆₁₀ ratio can sensitively reflect the activity of HsNMT1 in the linear range of 2-75 nM with a low detection limit of 0.56 nM. Moreover, the method was successfully applied for probing the HsNMT1 activities in different cell lysates and inhibitor screening. Furthermore, given the replaceability of the substrate peptide, the proposed assay is promising for universal application to other lipid transferases and exhibits great potential in lipid transferase-targeted drug development.

Dark-field hyperspectral imaging for label free detection of nano-bio-materials

Nanomaterials are playing an increasingly important role in cancer diagnosis and treatment. Nanoparticle (NP)-based technologies have been utilized for targeted drug delivery during chemotherapies, photodynamic therapy, and immunotherapy. Another active area of research is the toxicity studies of these nanomaterials to understand the cellular uptake and transport of these materials in cells, tissues, and environment. Traditional techniques such as transmission electron microscopy, and mass spectrometry to analyze NP-based cellular transport or toxicity effect are expensive, require extensive sample preparation, and are low-throughput. Dark-field hyperspectral imaging (DF-HSI), an integration of spectroscopy and microscopy/imaging, provides the ability to investigate cellular transport of these NPs and to quantify the distribution of them within bio-materials. DF-HSI also offers versatility in non-invasively monitoring microorganisms, single cell, and proteins. DF-HSI is a low-cost, label-free technique that is minimally invasive and is a viable choice for obtaining high-throughput quantitative molecular analyses. Multimodal imaging modalities such as Fourier transform infrared and Raman spectroscopy are also being integrated with HSI systems to enable chemical imaging of the samples. HSI technology is being applied in surgeries to obtain molecular information about the tissues in real-time. This article provides brief overview of fundamental principles of DF-HSI and its application for nanomaterials, protein-detection, single-cell analysis, microbiology, surgical procedures along with technical challenges and future integrative approach with other imaging and measurement modalities. This article is categorized under: Diagnostic Tools > in vitro Nanoparticle-Based Sensing Diagnostic Tools > in vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Fluorescence Method for the Detection of Protein Kinase Activity by Using a Zirconium-Based Metal-Organic Framework as an Affinity Probe

In cell-signaling pathways, protein kinases are critical and ubiquitous regulators. Abnormal kinase activity leads to many major diseases; therefore, simple and efficient methods for detecting protein kinases are in high demand. This study proposed a simple, rapid fluorescence-based sensor for protein kinase activity analysis, using the zirconium-based metal organic framework UiO-66 as a highly efficient affinity probe. UiO-66 has a large specific surface area, good stability, and a large number of Zr defect sites, which can efficiently identify phosphorylation sites. UiO-66 is an ideal nanoreactor that can efficiently enrich phosphorylated peptides. Under optimal experimental conditions, the increased fluorescence intensity was directly proportional to the protein kinase activity. The lower limit of detection was 0.00005 U·μL^-1. The assay could also be used for the screening of protein kinase inhibitors, could determine the activity of other kinds of kinases, and was universally applicable. This method was used for protein kinase activity detection in drug-stimulated MCF-7 cell lysates and demonstrated its potential applicability in kinase-related research.

Detection of casein kinase II by aggregation-induced emission

A novel aggregation-induced emission (AIE) probe comprised of a hydrophilic protein kinase specific peptide and a hydrophobic tetraphenylethene (TPE) unit was synthesized through click reaction. The prepared TPE-peptide probe could be completely degraded by carboxypeptidase Y (CPY) to release hydrophobic TPE part, which aggregated in buffer solution and showed strong TPE emission. In the presence of casein kinase (CKII), the phosphorylation of peptide prevented the complete degradation by CPY producing the nonemissive probe. Thus, the developed probe can be used to detect CKII homogeneously and conveniently. This detection process can be finished within 1.5 h with high sensitivity (0.05 mU/μL) and good selectivity. The developed method can also be used to screen protein kinase inhibitor even in a complex biological system.

A Water-Stable Luminescent Metal-Organic Framework for Rapid and Visible Sensing of Organophosphorus Pesticides

Metal-organic frameworks (MOFs) have shown considerable prospects for sensing pesticide residues. However, the low stability of MOFs in water hinders them from testing food and environmental samples. Herein, we report an easy and cost-efficient synthesis of a water-stable zirconium luminescent MOF (Zr-LMOF) and its application for rapid, sensitive, and in situ detection of organophosphorous pesticides (OPPs). The Zr-MOF is prepared using Zr(IV) and 1,2,4,5-tetrakis(4-carboxyphenyl)benzene. The synthesized Zr-LMOF rapidly absorbs trace amounts of OPP parathion-methyl and indicates its presence. A low limit of detection of 0.115 μg kg^-1 (0.438 nM) with a wide linear range from 70 μg kg^-1 to 5.0 mg kg^-1 was achieved. Satisfactory recoveries ranging from 78% to 107% were obtained for spiked food and environmental samples. Further, the Zr-LMOF was applied to imitate rapid and in situ imaging detection of pesticide residue on fresh produce nondestructively; visual signals appeared under ultraviolet light within 5 min. These results suggest that the Zr-LMOF has the potential for low-cost, rapid, and in situ imaging detection of OPPs contamination via easy-to-read visual signal.

Optical assays based on colloidal inorganic nanoparticles

Colloidal inorganic nanoparticles have wide applications in the detection of analytes and in biological assays. A large number of these assays rely on the ability of gold nanoparticles (AuNPs, in the 20 nm diameter size range) to undergo a color change from red to blue upon aggregation. AuNP assays can be based on cross-linking, non-cross linking or unmodified charge-based aggregation. Nucleic acid-based probes, monoclonal antibodies, and molecular-affinity agents can be attached by covalent or non-covalent means. Surface plasmon resonance and SERS techniques can be utilized. Silver NPs also have attractive optical properties (higher extinction coefficient). Combinations of AuNPs and AgNPs in nanocomposites can have additional advantages. Magnetic NPs and ZnO, TiO2 and ZnS as well as insulator NPs including SiO2 can be employed in colorimetric assays, and some can act as peroxidase mimics in catalytic applications. This review covers the synthesis and stabilization of inorganic NPs and their diverse applications in colorimetric and optical assays for analytes related to environmental contamination (metal ions and pesticides), and for early diagnosis and monitoring of diseases, using medically important biomarkers.

Copper nanoclusters/polydopamine nanospheres based fluorescence aptasensor for protein kinase activity determination

A fluorescence aptasensor was constructed for protein kinase (PKA) activity detection by utilizing copper nanoclusters (CuNCs) and polydopamine nanospheres (PDANS). Through the π-π stacking interactions between adenosine triphosphate (ATP) aptamer and PDANS, the ATP aptamer modified CuNCs (apt-CuNCs) were absorbed onto PDANS surface, thus the fluorescence of apt-CuNCs were quenched through fluorescence resonance energy transfer (FRET) from apt-CuNCs to PDANS. In the presence of ATP, ATP specifically bound to aptamer, causing the dissociation of apt-CuNCs from PDANS surface and restoring the fluorescence of apt-CuNCs. However, PKA translated ATP into adenosine diphosphate (ADP), and ADP had no competence to combine with ATP aptamer, thus, apt-CuNCs were released and absorbed onto the PDANS surface to cause the fluorescence quenching of apt-CuNCs again. Therefore, PKA activity was conveniently detected via the fluorescence signal change. Under the optimal conditions, PKA activity was detected in the range of 0.05-4.5 U mL^-1 with a detection limit of 0.021 U mL^-1. Furthermore, the feasibility of the aptasensor for kinase inhibitor screening was explored via assessment of kinase inhibitor H-89 as one model. This aptasensor was also performed for PKA activity determination in HepG2 cell lysates with satisfactory results.

Sensitive electrogenerated chemiluminescence biosensors for protein kinase activity analysis based on bimetallic catalysis signal amplification and recognition of Au and Pt loaded metal-organic frameworks nanocomposites

In this work, a novel and sensitive electrogenerated chemiluminescence (ECL) biosensor for protein kinase A (PKA) activity analysis and relevant inhibitor screening was proposed based on bimetallic catalysis signal amplification and recognition of Au and Pt nanoparticles loaded metal-organic frameworks (Au&Pt@UiO-66) nanocomposite. After being phosphorylated by PKA in the presence of ATP, Au&Pt@UiO-66 probes were specifically chelated to the modified electrode by forming Zr-O-P bonds between the surface defects of UiO-66 and the phosphorylated kemptide. Due to the high synergistic catalysis of Au&Pt@UiO-66 nanocomposites to the luminol-H₂O₂ reaction, the ECL signal of luminol was greatly enhanced. Moreover, UiO-66 afford numerous Zr defect sites for high efficient phosphate group recognition, and can also prevent the nanoparticles from aggregating during catalytic reactions. Thus, the excellent performance of the ECL biosensor with high sensitivity and superior stability was obtained. Under the optimized conditions, the detection limit for PKA activity was 0.009 UmL^-1 (S/N = 3). Meanwhile, the ECL biosensor was successfully applied in inhibitor screening and cell lysates PKA activity analysis, showing great promise in kinase related research.

Colorimetric sensor for cimetidine detection in human urine based on d-xylose protected gold nanoparticles

A simple, novel, and rapid colorimetric sensor for cimetidine (Cim) detection based on d-xylose protected gold nanoparticles (d-x@AuNPs) has been developed for the first time.

Facile and Sensitive Method for Protein Kinase A Activity Assay Based on Fluorescent Off-On PolyU-peptide Assembly

Phosphorylation mediated by protein kinases plays a pivotal role in metabolic and cell-signaling processes, and the dysfunction of protein kinases such as protein kinase A (PKA) may induce several human diseases. Therefore, it is of great significance to develop a facile and effective method for PKA activity assay and high-throughput screening of inhibitors. Herein, we develop a new fluorescent off-on method for PKA assay based on the assembly of anionic polyuridylic acid (polyU) and cationic fluorescent peptide. The phosphorylation of the peptide disrupts its electrostatic binding with polyU, suppresses the concentration quenching effect of polyU, and thus causes fluorescence recovery. The recovered fluorescence intensity at 585 nm is directly proportional to the PKA activity in the range of 0.1-3.2 U/mL with a detection limit of 0.05 U/mL. Using our method, the PKA activity in HeLa cell lysate is determined to be 58.2 ± 5.1 U/mg protein. The method has also been employed to evaluate the inhibitory effect of PKA inhibitors with satisfactory results and may be expected to be a promising candidate for facile and cost-effective assay of kinase activity and high-throughput inhibitor screening.

Point-of-care testing for streptomycin based on aptamer recognizing and digital image colorimetry by smartphone

The rapid detection of antibiotic residual in everyday life is very important for food safety. In order to realize the on-site and visual detection of antibiotic, a POCT method was established by using digital image colorimetry based on smartphone. Streptomycin was taken as the analyte model of antibiotics, streptomycin aptamer preferentially recognized analyte, and the excess aptamer hybridized with the complementary DNA to form the dsDNA. SYBR Green I combined with the dsDNA and then emitted obvious green fluorescence, thus the fluorescence intensity decreased with the increasing of streptomycin concentration. Then a smartphone-based device was constructed as the fluorescence readout. The smartphone camera acquired the images of the fluorescence derived from the samples, and the Touch Color APP installed in smartphone read out the RGB values of the images. There was a linear relationship between the G values and the streptomycin concentrations in the range of 0.1-100µM. The detection limit was 94nM, which was lower than the maximum residue limit defined by World Health Organization. The POCT method was applied for determining streptomycin in chicken and milk samples with recoveries in 94.1-110%. This method had the advantages of good selectivity, simple operation and on-site visualization.

Simple fluorescence-based detection of protein kinase A activity using a molecular beacon probe

Protein kinase A was detected by quantifying the amount of ATP used after a protein kinase reaction. The ATP assay was performed using the T4 DNA ligase and a molecular beacon (MB). In the presence of ATP, DNA ligase catalyzed the ligation of short DNA. The ligation product then hybridized to MB, resulting in a fluorescence enhancement of the MB. This assay was capable of determining protein kinase A in the range of 12.5∼150 nM, with a detection limit of 1.25 nM. Furthermore, this assay could also be used to investigate the effect of genistein on protein kinase A. It was a universal, non-radioisotopic, and homogeneous method for assaying protein kinase A.

Nanotechnology-Enhanced No-Wash Biosensors for in Vitro Diagnostics of Cancer

In vitro biosensors have been an integral component for early diagnosis of cancer in the clinic. Among them, no-wash biosensors, which only depend on the simple mixing of the signal generating probes and the sample solution without additional washing and separation steps, have been found to be particularly attractive. The outstanding advantages of facile, convenient, and rapid response of no-wash biosensors are especially suitable for point-of-care testing (POCT). One fast-growing field of no-wash biosensor design involves the usage of nanomaterials as signal amplification carriers or direct signal generating elements. The analytical capacity of no-wash biosensors with respect to sensitivity or limit of detection, specificity, stability, and multiplexing detection capacity is largely improved because of their large surface area, excellent optical, electrical, catalytic, and magnetic properties. This review provides a comprehensive overview of various nanomaterial-enhanced no-wash biosensing technologies and focuses on the analysis of the underlying mechanism of these technologies applied for the early detection of cancer biomarkers ranging from small molecules to proteins, and even whole cancerous cells. Representative examples are selected to demonstrate the proof-of-concept with promising applications for in vitro diagnostics of cancer. Finally, a brief discussion of common unresolved issues and a perspective outlook on the field are provided.

A Colorimetric Sensor for the Highly Selective Detection of Sulfide and 1,4-Dithiothreitol Based on the In Situ Formation of Silver Nanoparticles Using Dopamine

Hydrogen sulfide (H₂S) has attracted attention in biochemical research because it plays an important role in biosystems and has emerged as the third endogenous gaseous signaling compound along with nitric oxide (NO) and carbon monoxide (CO). Since H₂S is a kind of gaseous molecule, conventional approaches for H₂S detection are mostly based on the detection of sulfide (S^2-) for indirectly reflecting H₂S levels. Hence, there is a need for an accurate and reliable assay capable of determining sulfide in physiological systems. We report here a colorimetric, economic, and green method for sulfide anion detection using in situ formation of silver nanoparticles (AgNPs) using dopamine as a reducing and protecting agent. The changes in the AgNPs absorption response depend linearly on the concentration of Na₂S in the range from 2 to 15 μM, with a detection limit of 0.03 μM. Meanwhile, the morphological changes in AgNPs in the presence of S^2- and thiol compounds were characterized by transmission electron microscopy (TEM). The as-synthetized AgNPs demonstrate high selectivity, free from interference, especially by other thiol compounds such as cysteine and glutathione. Furthermore, the colorimetric sensor developed was applied to the analysis of sulfide in fetal bovine serum and spiked serum samples with good recovery.

Gold nanoparticles-based electrochemical method for the detection of protein kinase with a peptide-like inhibitor as the bioreceptor

This article presents a general method for the detection of protein kinase with a peptide-like kinase inhibitor as the bioreceptor, and it was done by converting gold nanoparticles (AuNPs)-based colorimetric assay into sensitive electrochemical analysis. In the colorimetric assay, the kinase-specific aptameric peptide triggered the aggregation of AuNPs in solution. However, the specific binding of peptide to the target protein (kinase) inhibited its ability to trigger the assembly of AuNPs. In the electrochemical analysis, peptides immobilized on a gold electrode and presented as solution triggered together the in situ formation of AuNPs-based network architecture on the electrode surface. Nevertheless, the formation of peptide-kinase complex on the electrode surface made the peptide-triggered AuNPs assembly difficult. Electrochemical impedance spectroscopy was used to measure the change in surface property in the binding events. When a ferrocene-labeled peptide (Fc-peptide) was used in this design, the network of AuNPs/Fc-peptide produced a good voltammetric signal. The competitive assay allowed for the detection of protein kinase A with a detection limit of 20 mU/mL. This work should be valuable for designing novel optical or electronic biosensors and likely lead to many detection applications.

Zirconium-metalloporphyrin frameworks as a three-in-one platform possessing oxygen nanocage, electron media, and bonding site for electrochemiluminescence protein kinase activity assay

A Zr-based metal-organic framework with zinc tetrakis(carboxyphenyl)-porphyrin (ZnTCPP) groups (MOF-525-Zn) was utilized to develop a novel electrochemiluminescence (ECL) biosensor for highly sensitive protein kinase activity assay. In this work, in terms of ECL measurements and cyclic voltammetry, the cathodic ECL behaviors of MOF-525-Zn in aqueous media were thoroughly investigated for the first time. The photoelectric active groups ZnTCPP on the MOF-525-Zn frameworks could promote the generation of singlet oxygen ((1)O2) via a series of electrochemical and chemical reactions, resulting in a strong and stable red irradiation at 634 nm. Additionally, the surfactant tetraoctylammonium bromide (TOAB) further facilitated dissolved oxygen to interact with the active sites ZnTCPP of MOF-525-Zn. Furthermore, the inorganic Zr-O clusters of MOF-525-Zn were simultaneously served as the recognition sites of phosphate groups. And then, an ultrasensitive ECL sensor was proposed for protein kinase A (PKA) activity detection with a linear range from 0.01 to 20 U mL(-1) and a sensitive detection limit of 0.005 U mL(-1). This biosensor can also be applied for quantitative kinase inhibitor screening. Finally, it exhibits good performance with high stability and acceptable fabrication reproducibility, which provide a valuable strategy for clinic diagnostics and therapeutics.

Colorimetric recognition of pazufloxacin mesilate based on the aggregation of gold nanoparticles

A novel colorimetric nanomaterial-assisted optical sensor for pazufloxacin mesilate was proposed for the first time. Pazufloxacin mesilate could induce the aggregation of glucose-reduced gold nanoparticles (AuNPs) through hydrogen-bonding interaction and electrostatic attraction, leading to the changes in color and absorption spectra of AuNPs. The effect of different factors such as pH, the amount of AuNPs, reaction time and reaction temperature was inspected. Under the optimum condition, UV-vis spectra showed that the absorption ratio (A670/A532) was linear with the concentration of pazufloxacin mesilate in the range from 9×10(-8) mol L(-1) to 7×10(-7) mol L(-1) with a linear coefficient of 0.9951. This method can be applied to detecting pazufloxacin mesilate with an ultralow detection limit of 7.92×10(-9) mol L(-1) without any complicated instruments. Through inspecting other analytes and ions, the anti-interference performance of AuNP detection system for pazufloxacin mesilate was excellent. For its high efficiency, rapid response rate as well as wide linear range, it had been successfully used to the analysis of pazufloxacin mesilate in human urine quantificationally.

A robust and quantitative assay platform for multiplexed, high throughput screening of protein kinase inhibitors

We present a new platform for multiplexed protein kinase activity assay using TiO₂decorated graphene oxide (GO), which is applicable to high throughput inhibitor screening.

Dye-Sensitized and Localized Surface Plasmon Resonance Enhanced Visible-Light Photoelectrochemical Biosensors for Highly Sensitive Analysis of Protein Kinase Activity

A novel visible-light photoelectrochemical (PEC) biosensor based on localized surface plasmon resonance (LSPR) enhancement and dye sensitization was fabricated for highly sensitive analysis of protein kinase activity with ultralow background. In this strategy, DNA conjugated gold nanoparticles (DNA@AuNPs) were assembled on the phosphorylated kemptide modified TiO2/ITO electrode through the chelation between Zr(4+) ions and phosphate groups, then followed by the intercalation of [Ru(bpy)3](2+) into DNA grooves. The adsorbed [Ru(bpy)3](2+) can harvest visible light to produce excited electrons that inject into the TiO2 conduction band to form photocurrent under visible light irradiation. In addition, the photocurrent efficiency was further improved by the LSPR of AuNPs under the irradiation of visible light. Moreover, because of the excellent conductivity and large surface area of AuNPs that facilitate electron-transfer and accommodate large number of [Ru(bpy)3](2+), the photocurrent was significantly amplified, affording an extremely sensitive PEC analysis of kinase activity with ultralow background signals. The detection limit of as-proposed PEC biosensor was 0.005 U mL(-1) (S/N = 3). The biosensor also showed excellent performances for quantitative kinase inhibitor screening and PKA activities detection in MCF-7 cell lysates under forskolin and ellagic acid stimulation. The developed dye-sensitization and LSPR enhancement visible-light PEC biosensor shows great potential in protein kinases-related clinical diagnosis and drug discovery.

Microextraction with phases containing nanoparticles

In this article, the state of the art of microextraction techniques that involve nanoparticles or nanomaterials (NPs) is reviewed, with special emphasis on the applications described in the biomedical field. The uses and advantages of the different types of NPs such as carbon nanotubes (either single- and multi-walled) and other carbon-based materials, metallic NPs, including gold, silver and magnetic NPs, and silica NPs are summarized. The main strategies used to modify the selectivity, extractive capacity and/or the stability of NPs through a chemical reaction are also reviewed. The potential advantages of NPs in different forms of off-line and on-line microextraction are discussed, and illustrative examples of application in the biomedical field are shown.