Nanochannels for diagnostic of thrombin-related diseases in human blood

Regeneratable bioinspired nanochannels for highly sensitive electrochemical detection of glycated albumin

Glycated albumin (GA) has been proposed as a reliable diabetes mellitus marker particularly useful in assessing intermediate glycemic control. Herein, we designed a bioinspired nanochannels for biochemical detection based on the host-guest interaction between β-cyclodextrin and azobenzene. Cyclodextrin was grafted on the inner surface of nanochannels of a nanoporous membrane and azobenzene was tagged to the terminal of GA aptamer, thereby facilitating the orientation of GA aptamer in the nanochannels. The presence of GA was monitored by recording the voltammetric signal of ferricyanide that transported across the nanochannel array. The peak current exhibited a linearity relationship with the GA concentration across a broad range of 1.0 ng mL-1 to 100 μg mL-1, along with a detection limit of 0.18 ng mL-1. Notably, the aptamer could be offloaded under ultraviolet light, regenerating the cyclodextrin functionalized nanochannels for subsequent re-immobilization of the fresh aptamer. The relative standard deviation for seven cycles of regeneration treatment was no more than 1.8 %. The remarkable reusability of the nanochannels offered a cost-effective, sensitive and reproducible aptasensing platform.

Solid-State Nanopore/Nanochannel Sensors with Enhanced Selectivity through Pore-in Modification

Nanopore sensing technology, as an emerging analytical method, has the advantages of simple operation, fast output, and label-free and has been widely used in fields such as protein analysis, gene sequencing, and biomarker detection. Inspired by biological ion channels, scientists have prepared various artificial solid-state nanopores/nanochannels. Biological ion channels have extremely high ion transport selectivity, while solid-state nanopores/nanochannels have poor selectivity. The selectivity of solid-state nanopores and nanochannels can be enhanced by modifying channel charge, varying pore size, incorporating specific chemical functionality, and adjusting operating (or solution) conditions. This Perspective highlights pore-in modification strategies for enhancing the selectivity of solid-state nanopore/nanochannel sensors by summarizing the articles published in the last 10 years. The future development prospects and challenges of pore-in modification in solid-state nanopore and nanochannel sensors are discussed. This Perspective helps readers better understand nanopore sensing technology, especially the importance of detection selectivity. We believe that solid-state nanopore/nanochannel sensors will soon enter our homes after various challenges.

SARS-CoV-2 Virus Detection Via a Polymeric Nanochannel-Based Electrochemical Biosensor

The development of simple, cost-effective, rapid, and quantitative diagnostic tools remains critical to monitor infectious COVID-19 disease. Although numerous diagnostic platforms, including rapid antigen tests, are developed and used, they suffer from limited accuracy, especially when tested with asymptomatic patients. Here, a unique approach to fabricate a nanochannel-based electrochemical biosensor that can detect the entire virion instead of virus fragments, is demonstrated. The sensing platform has uniform nanoscale channels created by the convective assembly of polystyrene (PS) beads on gold electrodes. The PS beads are then functionalized with bioreceptors while the gold surface is endowed with anti-fouling properties. When added to the biosensor, SARS-CoV-2 virus particles block the nanochannels by specific binding to the bioreceptors. The nanochannel blockage hinders the diffusion of a redox probe; and thus, allows quantification of the viral load by measuring the changes in the oxidation current before and after virus incubation. The biosensor shows a low limit of detection of ≈1.0 viral particle mL-1 with a wide detection range up to 108 particles mL-1 in cell culture media. Moreover, the biosensor is able to differentiate saliva samples with SARS-CoV-2 from those without, demonstrating the potential of this technology for translation into a point-of-care biosensor product.

Electrochemical monitoring of enzymatic cleavage in nanochannels with nanoparticle-based enhancement: determination of MMP-9 biomarker

For the first time the use of nanoparticles as carriers of an enzymatic substrate immobilized inside nanoporous alumina membranes is proposed with the aim of amplifying the nanochannel blocking produced and, consequently, improving the efficiency of an enzyme determination through enzymatic cleavage. Streptavidin-modified polystyrene nanoparticles (PSNPs) are proposed as carrier agents, contributing to the steric and the electrostatic blockage due to the charge they present at different pH values. Electrostatic blockage is the predominant effect that governs the blockage in the interior of the nanochannel and is dependent not just in the charge inside the channel, but also in the polarity of the redox indicator used. Hence, the effect of using negatively charged ([Fe(CN)₆]^4-) and positively charged ([Ru(NH₃)₆]³⁺) redox indicator ions is studied for the first time. Under the optimum conditions, matrix-metalloproteinase 9 (MMP-9) is detected at clinically relevant levels (100-1200 ng/mL) showing a detection limit of 75 ng/mL and a quantification limit of 251 ng/mL with good reproducibility (RSD: 8%) and selectivity, also showing an excellent performance in real samples with acceptable recovery percentages (in the range around 80-110%). Overall, our approach represents a cheap and fast sensing methodology of great potential in point-of-care diagnostics.

Functional DNA sensors integrated with nucleic acid signal amplification strategies for non-nucleic acid targets detection

In addition to carrying and transmitting genetic material, some DNA molecules have specific binding ability or catalytic function. DNA with this special function is collectively referred to as functional DNA (fDNA), such as aptamer, DNAzyme and so on. fDNA has the advantages of simple synthetic process, low cost and low toxicity. It also has high chemical stability, recognition specificity and biocompatibility. In recent years, fDNA biosensors have been widely investigated as signal recognition elements and signal transduction elements for the detection of non-nucleic acid targets. However, the main problem of fDNA sensors is their limited sensitivity to trace targets, especially when the affinity of fDNA to the targets is low. To further improve the sensitivity, various nucleic acid signal amplification strategies (NASAS) are explored to improve the limit of detection of fDNA. In this review, we will introduce four NASAS (hybridization chain reaction, entropy-driven catalysis, rolling circle amplification, CRISPR/Cas system) and the corresponding design principles. The principle and application of these fDNA sensors integrated with signal amplification strategies for detection of non-nucleic acid targets are summarized. Finally, the main challenges and application prospects of NASAS integrated fDNA biosensing system are discussed.

Biomimetic nanochannels for molybdate transport: application to sensitive electrochemical immunoassay for HER2

A nanochannel-based electrochemical immunoassay was developed for the detection of human epidermal growth factor receptor 2 (HER2), with molybdate as the reporter to explore the interaction occurring into the nanochannels. The presence of target increased steric hindrance of the antibody-functionalized nanochannels, thereby hindering the transport of molybdate. And the reporter could be monitored by working electrode modified with hydroxyapatite nanoparticles, based on the formation of the redox-active molybdophosphate. As a result, peak current obtained at ca. - 0.28 V in square wave voltammograms could be applied to quantitative determination of HER2. The electrochemical signal increased linearly with the logarithm of the concentration of HER2 in a broad dynamic range of 0.1 pg∙mL^-1 to 10 ng∙mL^-1 with a detection limit of 0.05 pg∙mL^-1. The reliability of this immunoassay was validated by a recovery range of 99.5% to 111.7% for the detection of three different levels of HER2 in human serum samples. Integrating with multiple bionanochannels, this immunoassay is expected to provide a versatile approach for quantitative detection of various biomarkers in related disease diagnosis and therapy.

Comparison of Optical and Electrical Sensor Characteristics for Efficient Analysis of Attachment and Detachment of Aptamer

Nucleic acid aptamer-based research has focused on achieving the highest performance for bioassays. However, there are limitations in evaluating the affinity for the target analytes in these nucleic acid aptamer-based bioassays. In this study, we mainly propose graphene oxide (GO)-based electrical and optical analyses to efficiently evaluate the affinity between an aptamer and its target. We found that an aptamer-coupled GO-based chip with an electrical resistance induced by a field-effect transistor, with aptamers as low as 100 pM, can detect the target, thrombin, at yields as low as 250 pM within five minutes. In the optical approach, the fluorescent dye-linked aptamer, as low as 100 nM, was efficiently used with GO, enabling the sensitive detection of thrombin at yields as low as 5 nM. The cantilever type of mechanical analysis also demonstrated the intuitive aptamer-thrombin reaction in the signal using dBm units. Finally, a comparison of electrical and optical sensors' characteristics was introduced in the attachment and detachment of aptamer to propose an efficient analysis that can be utilized for various aptamer-based research fields.

Incorporation of a Multi-Valent Aptamer into Electrochemical Biosensors to Achieve an Improved Performance for Thrombin Analysis in Blood Serum

The electrochemical aptamer-based (E-AB) biosensor usually has a long reaction time when detecting thrombin. This work reports the design of an E-AB biosensor with dual recognition sites to quickly detect thrombin. Specifically, two specific recognition sites of thrombin were used to design three aptamer sequences (TBA-15, TBA-29 and TBA-U), followed by fabrication of corresponding sensors. First, we tested these three types of biosensors in tris buffer solution, and found that the response time of the TBA-U sensor to the same concentration of thrombin was about 2 hours, which is shorter than TBA-15 and TBA-29 sensors. Then, we also did the same test in 50 % diluted serum with 500 nM thrombin. The response time of the TBA-U sensor was about 2 hours, which is still faster than the 3 hours of TBA-15 sensor and the 5.5 hours for TBA-29 sensor. In addition, in terms of dynamic range and specificity, TBA-U has good performance.

A protocol to measure slow protein dynamics of the cholera toxin B pentamers using broadband dielectric spectroscopy

The present protocol describes how to measure experimentally the slow protein dynamics that take place upon the thermal unfolding of the B subunit cholera toxin pentamers using broadband dielectric spectroscopy (BDS) in weakly hydrated and nanoconfined conditions. Transient unfolding intermediates, rarely identified otherwise, are revealed thanks to the B subunit's remarkable heat resistance up to 180°C and distinct molecular dynamics. The frequencies detected experimentally are consistent with the spatiotemporal scales of motions of molecular dynamics simulation.

For complete details on the use and execution of this protocol, please refer to Bourgeat et al. (2021, 2019).

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Measure protein dynamics experimentally using BDS in nanoconfined conditions

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Identify rare cholera toxin B subunit assembly and unfolding intermediates

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Detect cholera toxin B subunits in temperatures up to 180°C

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Match between protein molecular dynamics from experiments and simulations

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Electrochemical Biosensors Based on Convectively Assembled Colloidal Crystals

Rapid, sensitive, selective and portable virus detection is in high demand globally. However, differentiating non-infectious viral particles from intact/infectious viruses is still a rarely satisfied sensing requirement. Using the negative space within monolayers of polystyrene (PS) spheres deposited directly on gold electrodes, we fabricated tuneable nanochannels decorated with target-selective bioreceptors that facilitate the size-selective detection of intact viruses. Detection occurred through selective nanochannel blockage of diffusion of a redox probe, [Fe(CN)6]3/4-, allowing a quantifiable change in the oxidation current before and after analyte binding to the bioreceptor immobilised on the spheres. Our model system involved partial surface passivation of the mono-assembled PS spheres, by silica glancing angle deposition, to confine bioreceptor immobilisation specifically to the channels and improve particle detection sensitivity. Virus detection was first optimised and modelled with biotinylated gold nanoparticles, recognised by streptavidin immobilised on the PS layer, reaching a low limit of detection of 37 particles/mL. Intact, label-free virus detection was demonstrated using MS2 bacteriophage (~23-28 nm), a marker of microbiological contamination, showing an excellent limit of detection of ~1.0 pfu/mL. Tuneable nanochannel geometries constructed directly on sensing electrodes offer label-free, sensitive, and cost-efficient point-of-care biosensing platforms that could be applied for a wide range of viruses.

Electrical monitoring of infection biomarkers in chronic wounds using nanochannels

Chronic wounds represent an important healthcare challenge in developed countries, being wound infection a serious complication with significant impact on patients' life conditions. However, there is a lack of methods allowing an early diagnosis of infection and a right decision making for a correct treatment. In this context, we propose a novel methodology for the electrical monitoring of infection biomarkers in chronic wound exudates, using nanoporous alumina membranes. Lysozyme, an enzyme produced by the human immune system indicating wound infection, is selected as a model compound to prove the concept. Peptidoglycan, a component of the bacterial layer and the native substrate of lysozyme, is immobilized on the inner walls of the nanochannels, blocking them both sterically and electrostatically. The steric blocking is dependent on the pore size (20-100 nm) and the peptidoglycan concentration, whereas the electrostatic blocking depends on the pH. The proposed analytical method is based on the electrical monitoring of the steric/electrostatic nanochannels unblocking upon the specific degradation of peptidoglycan by lysozyme, allowing to detect the infection biomarker at 280 ng/mL levels, which are below those expected in wounds. The low protein adsorption rate and thus outstanding filtering properties of the nanoporous alumina membranes allowed us to discriminate wound exudates from patients with both sterile and infected ulcers without any sample pre-treatment usually indispensable in most diagnostic devices for analysis of physiological fluids. Although size and charge effects in nanochannels have been previously approached for biosensing purposes, as far as we know, the use of nanoporous membranes for monitoring enzymatic cleavage processes, leading to analytical systems for the specific detection of the enzymes has not been deeply explored so far. Compared with previously reported methods, our methodology presents the advantages of no need of neither bioreceptors (antibodies or aptamers) nor competitive assays, low matrix effects and quantitative and rapid analysis at the point-of-care, being also of potential application for the determination of other protease biomarkers.

Impedance-Based Nanoporous Anodized Alumina/ITO Platforms for Label-Free Biosensors

We report an experimental and computational approach for the fabrication and characterization of a highly sensitive and responsive label-free biosensor that does not require the presence of redox couples in electrolytes for sensitive electrochemical detection. The sensor is based on an aptamer-functionalized transparent electrode composed of nanoporous anodized alumina (NAA) grown on indium tin oxide (ITO)-covered glass. Electrochemical impedance changes in a thrombin binding aptamer (TBA)-functionalized NAA/ITO/glass electrode due to specific binding of α-thrombin are monitored for protein detection. The aptamer-functionalized electrode enables sensitive and specific thrombin protein detection with a detection limit of ∼10 pM and a high signal-to-noise ratio. The transient impedance of the alumina film-covered surface is computed using a computational electrochemical impedance spectroscopy (EIS) approach and compared to experimental observations to identify the dominant mechanisms underlying the sensor response. The computational and experimental results indicate that the sensing response is due to the modified ionic transport under the combined influence of steric hindrance and surface charge modification due to ligand/receptor binding between α-thrombin and the aptamer-covered alumina film. These results suggest that alumina film-covered electrodes utilize both steric and charge modulation for sensing, leading to tremendous improvement in the sensitivity and signal-to-noise ratio. The film configuration is amenable for miniaturization and can be readily incorporated into existing portable sensing systems.

Nanoconfinement Effect for Signal Amplification in Electrochemical Analysis and Sensing

Owing to the urgent need for electrochemical analysis and sensing of trace target molecules in various fields such as medical diagnosis, agriculture and food safety, and environmental monitoring, signal amplification is key to promoting analysis and sensing performance. The nanoconfinement effect, derived from nanoconfined spaces and interfaces with sizes approaching those of target molecules, has witnessed rapid development for ultra-sensitive analyzing and sensing. In this review, the two main types of nanoconfinement systems - confined nanochannels and planes - are assessed and recent progress is highlighted. The merits of each nanoconfinement system, the nanoconfinement effect mechanisms, and applications for electrochemical analysis and sensing are summarized and discussed. This review aims to help deepen the understanding of nanoconfinement devices and their effects in order to develop new analysis and sensing applications for researchers in various fields.

Bioinspired Solid-State Nanochannel Sensors: From Ionic Current Signals, Current, and Fluorescence Dual Signals to Faraday Current Signals

Inspired from bioprotein channels of living organisms, constructing "abiotic" analogues, solid-state nanochannels, to achieve "smart" sensing towards various targets, is highly seductive. When encountered with certain stimuli, dynamic switch of terminal modified probes in terms of surface charge, conformation, fluorescence property, electric potential as well as wettability can be monitored via transmembrane ionic current, fluorescence intensity, faraday current signals of nanochannels and so on. Herein, the modification methodologies of nanochannels and targets-detecting application are summarized in ions, small molecules, as well as biomolecules, and systematically reviewed are the nanochannel-based detection means including 1) by transmembrane current signals; 2) by the coordination of current- and fluorescence-dual signals; 3) by faraday current signals from nanochannel-based electrode. The coordination of current and fluorescence dual signals offers great benefits for synchronous temporal and spatial monitoring. Faraday signals enable the nanoelectrode to monitor both redox and non-redox components. Notably, by incorporation with confined effect of tip region of a needle-like nanopipette, glorious in-vivo monitoring is conferred on the nanopipette detector at high temporal-spatial resolution. In addition, some outlooks for future application in reliable practical samples analysis and leading research endeavors in the related fantastic fields are provided.

Discrimination of α-Thrombin and γ-Thrombin Using Aptamer-Functionalized Nanopore Sensing

Protein detection and identification at the single-molecule level are major challenges in many biotechnological fields. Solid-state nanopores have raised attention as label-free biosensors with high sensitivity. Here, we use solid-state nanopore sensing to discriminate two closely related proteins, α-thrombin and γ-thrombin. We show that aptamer functionalization improves protein discrimination thanks to a significant difference in the relative current blockade amplitude. To enhance discrimination, we postprocessed the signals using machine learning and training algorithms and we were able to reach an accuracy of 98.8% using seven features and ensemble methods.

Self-ordered anodic porous alumina with inter-hole spacing over 1.5 μm

Self-ordered anodic porous alumina with inter-hole spacing of 1.8 μm.

Porous Alumina Membrane-Based Electrochemical Biosensor for Protein Biomarker Detection in Chronic Wounds

A label-free electrochemical detection platform for the sensitive and rapid detection of Flightless I (Flii) protein, a biomarker of wound chronicity, has been developed using nanoporous anodic alumina (NAA) membranes modified with Flii antibody recognition sites. The electrochemical detection is based on the nanochannel blockage experienced upon Flii capture by immobilized antibodies within the nanochannels. This capture impedes the diffusion of redox species [[Fe(CN)₆]^4-/3-] toward a gold electrode attached at the backside of the modified NAA membrane. Partial blockage causes a decrease in the oxidation current of the redox species at the electrode surface which is used as an analytical signal by the reported biosensor. The resulting biosensing system allows detection of Flii at the levels found in wounds. Two types of assays were tested, sandwich and direct, showing <3 and 2 h analysis time, respectively, a significant reduction in time from the nearly 48 h required for the conventional Western blot assay. Slightly higher sensitivity values were observed for the sandwich-based strategy. With faster analysis, lack of matrix effects, robustness, ease of use and cost-effectiveness, the developed sensing platform has the potential to be translated into a point-of-care (POC) device for chronic wound management and as a simple alternative characterization tool in Flii research.

Nanoparticles as Emerging Labels in Electrochemical Immunosensors

This review shows recent trends in the use of nanoparticles as labels for electrochemical immunosensing applications. Some general considerations on the principles of both the direct detection based on redox properties and indirect detection through electrocatalytic properties, before focusing on the applications for mainly proteins detection, are given. Emerging use as blocking tags in nanochannels-based immunosensing systems is also covered in this review. Finally, aspects related to the analytical performance of the developed devices together with prospects for future improvements and applications are discussed.

Biomolecule-Functionalized Solid-State Ion Nanochannels/Nanopores: Features and Techniques

Solid-state ion nanochannels/nanopores, the biomimetic products of biological ion channels, are promising materials in real-world applications due to their robust mechanical and controllable chemical properties. Functionalizations of solid-state ion nanochannels/nanopores by biomolecules pave a wide way for the introduction of varied properties from biomolecules to solid-state ion nanochannels/nanopores, making them smart in response to analytes or external stimuli and regulating the transport of ions/molecules. In this review, two features for nanochannels/nanopores functionalized by biomolecules are abstracted, i.e., specificity and signal amplification. Both of the two features are demonstrated from three kinds of nanochannels/nanopores: nucleic acid-functionalized nanochannels/nanopores, protein-functionalized nanochannels/nanopores, and small biomolecule-functionalized nanochannels/nanopores, respectively. Meanwhile, the fundamental mechanisms of these combinations between biomolecules and nanochannels/nanopores are explored, providing reasonable constructs for applications in sensing, transport, and energy conversion. And then, the techniques of functionalizations and the basic principle about biomolecules onto the solid-state ion nanochannels/nanopores are summarized. Finally, some views about the future developments of the biomolecule-functionalized nanochannels/nanopores are proposed.

Magnetic Nanoparticles Enhance Pore Blockage-Based Electrochemical Detection of a Wound Biomarker

A novel pore blockage-based electrochemical immunosensor based on the combination of 100 nm-magnetic nanoparticles (MNPs), as signal enhancers, and 200 nm-pore diameter nanoporous anodic alumina (NAA) membranes, as sensing platform, is reported. A peptide conjugate mimicking flightless I (Flii), a wound healing biomarker, was chosen as target analyte. The sensing platform consists of an anti-Flii antibody (Ab1)-modified NAA membrane attached onto a gold electrode. Anti-KLH antibody (Ab2)-modified MNPs (MNP-Ab2) were used to selectively capture the Flii peptide conjugate in solution. Sensing was based on pore blockage of the Ab1-modified NAA membrane caused upon specific binding of the MNP-Ab2-analyte complex. The degree of pore blockage, and thus the concentration of the Flii peptide conjugate in the sample, was measured as a reduction in the oxidation current of a redox species ([Fe(CN)6]4-) added in solution. We demonstrated that pore blockage is drastically enhanced by applying an external magnetic field at the membrane backside to facilitate access of the MNP-Ab2-analyte complex into the pores, and thus ensure its availability to bind to the Ab1-modified NAA membrane. Combining the pore blockage-based electrochemical magnetoimmunosensor with an externally applied magnetic field, a limit of detection (LOD) of 0.5 ng/ml of Flii peptide conjugate was achieved, while sensing in the absence of magnetic field could only attain a LOD of 1.2 μg/ml. The developed sensing strategy is envisaged as a powerful solution for the ultra-sensitive detection of an analyte of interest present in a complex matrix.

Label free thrombin detection in presence of high concentration of albumin using an aptamer-functionalized nanoporous membrane

Nanoporous alumina membranes have become a ubiquitous biosensing platform for a variety of applications and aptamers are being increasingly utilized as recognition elements in protein sensing devices. Combining the advantages of the two, we report label-free sensitive detection of human α-thrombin by an aptamer-functionalized nanoporous alumina membrane using a four-electrode electrochemical cell. The sensor response to α-thrombin was determined in the presence of a high concentration (500 μM) of human serum albumin (HSA) as an interfering protein in the background. The sensor sensitivity was also characterized against γ-thrombin, which is a modified α-thrombin lacking the aptamer binding epitope. The detection limit, within an appreciable signal/noise ratio, was 10 pM of α-thrombin in presence of 500 μM HSA. The proposed scheme involves the use of minimum reagents/sample preparation steps, has appreciable response in presence of high concentrations of interfering molecules and is readily amenable to miniaturization by association with existing-chip based electrical systems for application in point-of-care diagnostic devices.

Proximity ligation assay induced and DNAzyme powered DNA motor for fluorescent detection of thrombin

A novel DNA motor for thrombin detection was described here based on proximity ligation assay (PLA) induced DNAzyme recycling cleavage. Fluorophore labeled DNA is modified on gold nanoparticles (AuNPs) and the fluorescent signal is quenched by AuNPs. The PLA between target thrombin and two aptamers induces the forming of Mg²⁺-dependent DNAzyme. The fluorophore labeled DNA is cleaved circularly by the DNAzyme, releasing the fluorescent fragment from AuNPs surface. The cleavage and rebinding process create a processive walking along AuNPs surface track. As a result, the fluorescent intensity recovers significantly. A good linear relationship is obtained between the ratio of fluorescence intensity and thrombin concentration in the range from 10 pM to 10 nM. The limit of detection is calculated to be 4 pM. These results are comparable or even better than other amplification based methods.

Detection of PARP-1 activity based on hyperbranched-poly (ADP-ribose) polymers responsive current in artificial nanochannels

The cellular enzyme poly ADP (ADP: adenosine diphosphate)-ribose polymerase-1 (PARP-1) plays key roles in DNA repair. Its activity is closely related to various cancer developments. Detection of PARP-1 activity is significant, however, it is relatively difficult since it lacks superiority property that can be used to detect conveniently. PARP-1 lead to the synthesis of hyperbranched poly (ADP-ribose) polymers (PAR) using nicotinamide adenine dinucleotide (NAD⁺) as substrate during DNA damage repairing. In this paper, we found that hyper-branched PAR increased the steric hindrance and reduced the flux of probe ions effectively in anodic aluminum oxide (AAO) nanochannels. To the best of our knowledge, few papers have been reported that hyper-branched polymer has the similar effects in nanochannels as G-quadruplex DNA. Thus, a novel and simple strategy for PARP-1 detection has been proposed due to its great impacts on the diffusion flux of ferricyanide in AAO. It is also proved that electrostatic repulsion is another important factor to influence the current. The method is label-free, simple and sensitive. Quantitative detection of PARP-1 activity was achieved with the detection limit of 0.006 U, which is lower or comparable to the most reported methods. The method has good accuracy and reproducibility. The strategy has been used to detect PARP-1 activity in real breast cancer cells and to evaluate PARP-1 inhibitors with satisfactory results, indicating that it is a potential powerful tool for clinical diagnosis and drug development in the future.

Advances in Nanoporous Anodic Alumina-Based Biosensors to Detect Biomarkers of Clinical Significance: A Review

There is a strong and growing demand for compact, portable, rapid, and low-cost devices to detect biomarkers of interest in clinical and point-of-care diagnostics. Such devices aid in early diagnosis of diseases without the need to rely on expensive and time-consuming large instruments in dedicated laboratories. Over the last decade, numerous biosensors have been developed for detection of a wide range of clinical biomarkers including proteins, nucleic acids, growth factors, and bacterial enzymes. Various transduction techniques have been reported based on biosensor technology that deliver substantial advances in analytical performance, including sensitivity, reproducibility, selectivity, and speed for monitoring a wide range of human health conditions. Nanoporous anodic alumina (NAA) has been used extensively for biosensing applications due to its inherent optical and electrochemical properties, ease of fabrication, large surface area, tunable properties, and high stability in aqueous environment. This review focuses on NAA-based biosensing systems for detection of clinically significant biomarkers using various detection techniques with the main focus being on electrochemical and optical transduction methods. The review covers an overview of the importance of biosensors for biomarkers detection, general (surface and structural) properties and fabrication of NAA, and NAA-based biomarker sensing systems.

Nanostructured Electrochemical Biosensors for Label-Free Detection of Water- and Food-Borne Pathogens

The emergence of nanostructured materials has opened new horizons in the development of next generation biosensors. Being able to control the design of the electrode interface at the nanoscale combined with the intrinsic characteristics of the nanomaterials engenders novel biosensing platforms with improved capabilities. The purpose of this review is to provide a comprehensive and critical overview of the latest trends in emerging nanostructured electrochemical biosensors. A detailed description and discussion of recent approaches to construct label-free electrochemical nanostructured electrodes is given with special focus on pathogen detection for environmental monitoring and food safety. This includes the use of nanoscale materials such as nanotubes, nanowires, nanoparticles, and nanosheets as well as porous nanostructured materials including nanoporous anodic alumina, mesoporous silica, porous silicon, and polystyrene nanochannels. These platforms may pave the way toward the development of point-of-care portable electronic devices for applications ranging from environmental analysis to biomedical diagnostics.

In situ monitoring of PTHLH secretion in neuroblastoma cells cultured onto nanoporous membranes

In this work, we propose for the first time the use of anodic aluminum oxide (AAO) nanoporous membranes for in situ monitoring of parathyroid hormone-like hormone (PTHLH) secretion in cultured human cells. The biosensing system is based on the nanochannels blockage upon immunocomplex formation, which is electrically monitored through the voltammetric oxidation of Prussian blue nanoparticles (PBNPs). Models evaluated include a neuroblastoma cell line (SK-N-AS) and immortalized keratinocytes (HaCaT) as a control of high PTHLH production. The effect of total number of seeded cells and incubation time on the secreted PTHLH levels is assessed, finding that secreted PTHLH levels range from approximately 60 to 400 ng/mL. Moreover, our methodology is also applied to analyse PTHLH production following PTHLH gene knockdown upon transient cell transfection with a specific silencing RNA (siRNA). Given that inhibition of PTHLH secretion reduces cell proliferation, survival and invasiveness in a number of tumors, our system provides a powerful tool for the preclinical evaluation of therapies that regulate PTHLH production. This nanoporous membrane - based sensing technology might be useful to monitor the active secretion of other proteins as well, thus contributing to characterize their regulation and function.

Asymmetric Nanochannel-Ionchannel Hybrid for Ultrasensitive and Label-Free Detection of Copper Ions in Blood

Nanochannel/nanopre based analysis methods have attracted increasing interest in recent years due to their exquisite ability to reveal changes in molecular volume. In this work, a highly asymmetric nanochannel-ionchannel hybrid coupled with an electrochemical technique was developed for copper ion (Cu²⁺) detection. Polyglutamic acid (PGA) was modified in a nanochannel array of porous anodic alumina (PAA). When different concentrations of Cu²⁺ were introduced into the nanochannel-ionchannel hybrid in a neutral environment, a Cu²⁺-PGA chelation reaction occurs, resulting in varied current-potential (I-V) properties of the nanochannel-ionchannel hybrid. When PAA was immersed in a low pH solution, the Cu²⁺-PGA complex dissociated. On the basis of the change in ionic current, a label-free assay for Cu²⁺ was achieved along with the ability to regenerate and reuse the constructed platform. Because of the unique mass transfer property of the nanochannel-ionchannel hybrid combined with the highly amplified ionic current magnitude of the nanochannel array, significantly increased assay sensitivity was achieved, as expected. To evaluate the applicability of the present methodology for detecting Cu²⁺ in a real sample, the Cu²⁺ content in real blood samples was analyzed. The results demonstrate that the present method shows excellent selectivity with high sensitivity toward Cu²⁺ detection in real blood samples.

High-performance and versatile electrochemical aptasensor based on self-supported nanoporous gold microelectrode and enzyme-induced signal amplification

Herein, novel and versatile electrochemical aptasensors were constructed on a self-supported nanoporous gold (np-Au) microelectrode, integrating with an exonuclease III (Exo III) induced signal amplification strategy. Self-supported np-Au microelectrode with 3D bicontinuous nanoporous structures possesses tremendously large specific area, clean surface, high stability and biocompatibility, bringing about significant advantages in both molecular recognition and signal response. As paradigms, two analytes of bisphenol A (BPA) and ochratoxin A (OTA) were selected to demonstrate the superiority and versatility of designed aptasensors. Trace amounts of mDNA (associated with BPA or OTA concentration) hybridized with cDNA strands assembled on np-Au microelectrode, activating the cleavage reaction with Exo III. Thus, cDNA was digested and mDNA was released to undergo a new hybridization and cleavage cycle. Finally, residual cDNA strands were recognized by methylene blue labelled rDNA/AuNPs with the assistance of hDNA to generate the electrochemical signals, which were used to quantitatively monitor targets. Under the optimized conditions, prepared aptasensors exhibited wide linear ranges (25pg/mL to 2ng/mL for BPA, 10pg/mL to 5ng/mL for OTA) with ultralow detection limits (10pg/mL for BPA, 5pg/mL for OTA), excellent selectivity and stability, and reliable detection in real samples. This work opens a new horizon for constructing promising electrochemical aptasensors for environmental monitoring, medical diagnostics and food safety.

Nanopore biosensor for sensitive and label-free nucleic acid detection based on hybridization chain reaction amplification

A label-free nanopore biosensor for detection of DNA target is proposed utilizing hybridization chain reaction (HCR) strategy for signal amplification. The DNA target triggered HCR to form large DNA nanostructure inside the nanopore and out the nanopore membrane, which inducing the ionic current decrease effectively due to the blockage of the nanopore. The developed method achieves a desirable sensitivity of 30fM with a wide linear dynamic range from 0.1 to 10pM and demonstrated good application for real sample analysis. This work has great potential to be applied in the early diagnosis of gene-related diseases and provide a new paradigm for label-free nucleic acid amplification strategy in ultrasensitive nanopore biosensor.

A Nanoporous Alumina Membrane Based Electrochemical Biosensor for Histamine Determination with Biofunctionalized Magnetic Nanoparticles Concentration and Signal Amplification

Histamine is an indicator of food quality and indispensable in the efficient functioning of various physiological systems. Rapid and sensitive determination of histamine is urgently needed in food analysis and clinical diagnostics. Traditional histamine detection methods require qualified personnel, need complex operation processes, and are time-consuming. In this study, a biofunctionalized nanoporous alumina membrane based electrochemical biosensor with magnetic nanoparticles (MNPs) concentration and signal amplification was developed for histamine determination. Nanoporous alumina membranes were modified by anti-histamine antibody and integrated into polydimethylsiloxane (PDMS) chambers. The specific antibody modified MNPs were used to concentrate histamine from samples and transferred to the antibody modified nanoporous membrane. The MNPs conjugated to histamine were captured in the nanopores via specific reaction between histamine and anti-histamine antibody, resulting in a blocking effect that was amplified by MNPs in the nanopores. The blockage signals could be measured by electrochemical impedance spectroscopy across the nanoporous alumina membrane. The sensing platform had great sensitivity and the limit of detection (LOD) reached as low as 3 nM. This biosensor could be successfully applied for histamine determination in saury that was stored in frozen conditions for different hours, presenting a potentially novel, sensitive, and specific sensing system for food quality assessment and safety support.

Simple and Versatile Detection of Viruses Using Anodized Alumina Membranes

A simple sensor for viral particles based on ionic conductivity through anodized alumina membranes was demonstrated using MS2 bacteriophage as an example. A facile two-point measuring scheme is geared toward realization using a computer's sound card input/output capabilities suitable for a fast and inexpensive point of care testing. The lowest detection concentration down to ~7 pfu/mL and a large dynamic range up to ~2000 pfu/mL were obtained due to physical optimization that included proper length and diameter for the pores, removing the oxide layer at the electrode, as well as the chemical optimization of covalent binding of antibodies to the pore's walls.

Nanobiosensors in diagnostics

Medical diagnosis has been greatly improved thanks to the development of new techniques capable of performing very sensitive detection and quantifying certain parameters. These parameters can be correlated with the presence of specific molecules and their quantity. Unfortunately, these techniques are demanding, expensive, and often complicated. On the other side, progress in other fields of science and technology has contributed to the rapid growth of nanotechnology. Although being an emerging discipline, nanotechnology has raised huge interest and expectations. Most of the enthusiasm comes from new possibilities and properties of nanomaterials. Biosensors (simple, robust, sensitive, cost-effective) combined with nanomaterials, also called nanobiosensors, are serving as bridge between advanced detection/diagnostics and daily/routine tests. Here we review some of the latest applications of nanobiosensors in diagnostics field.

Ultra-high-density 3D DNA arrays within nanoporous biocompatible membranes for single-molecule-level detection and purification of circulating nucleic acids

Extracellular nucleic acids freely circulating in blood and other physiologic fluids are important biomarkers for non-invasive diagnostics and early detection of cancer and other diseases, yet difficult to detect because they exist in very low concentrations and large volumes. Here we demonstrate a new broad-range sensor platform for ultrasensitive and selective detection of circulating DNA down to the single-molecule level. The biosensor is based on a chemically functionalized nanoporous diamond-like carbon (DLC) coated alumina membrane. The few nanometer-thick, yet perfect and continuous DLC-coating confers the chemical stability and biocompatibility of the sensor, allowing its direct application in biological conditions. The selective detection is based on complementary hybridization of a fluorescently-tagged circulating cancer oncomarker (a 21-mer nucleic acid) with covalently immobilized DNA on the surface of the membrane. The captured DNAs are detected in the nanoporous structure of the sensor using confocal scanning laser microscopy. The flow-through membrane sensor demonstrates broad-range sensitivity, spanning from 10(15) molecules per cm(2) down to single molecules, which is several orders of magnitude improvement compared to the flat DNA microarrays. Our study suggests that these flow-through type nanoporous sensors represent a new powerful platform for large volume sampling and ultrasensitive detection of different chemical biomarkers.