A label-free immunosensor array using single-chain antibody fragments

Advancement in COVID-19 detection using nanomaterial-based biosensors

Coronavirus disease 2019 (COVID-19) pandemic has exemplified how viral growth and transmission are a significant threat to global biosecurity. The early detection and treatment of viral infections is the top priority to prevent fresh waves and control the pandemic. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified through several conventional molecular methodologies that are time-consuming and require high-skill labor, apparatus, and biochemical reagents but have a low detection accuracy. These bottlenecks hamper conventional methods from resolving the COVID-19 emergency. However, interdisciplinary advances in nanomaterials and biotechnology, such as nanomaterials-based biosensors, have opened new avenues for rapid and ultrasensitive detection of pathogens in the field of healthcare. Many updated nanomaterials-based biosensors, namely electrochemical, field-effect transistor, plasmonic, and colorimetric biosensors, employ nucleic acid and antigen-antibody interactions for SARS-CoV-2 detection in a highly efficient, reliable, sensitive, and rapid manner. This systematic review summarizes the mechanisms and characteristics of nanomaterials-based biosensors for SARS-CoV-2 detection. Moreover, continuing challenges and emerging trends in biosensor development are also discussed.

Relay-type sensing mode: A strategy to push the limit on nanomechanical sensor sensitivity based on the magneto lever

Ultrasensitive molecular detection and quantization are crucial for many applications including clinical diagnostics, functional proteomics, and drug discovery; however, conventional biochemical sensors cannot satisfy the stringent requirements, and this has resulted in a long-standing dilemma regarding sensitivity improvement. To this end, we have developed an ultrasensitive relay-type nanomechanical sensor based on a magneto lever. By establishing the link between very weak molecular interaction and five orders of magnitude larger magnetic force, analytes at ultratrace level can produce a clearly observable mechanical response. Initially, proof-of-concept studies showed an improved detection limit up to five orders of magnitude when employing the magneto lever, as compared with direct detection using probe alone. In this study, we subsequently demonstrated that the relay-type sensing mode was universal in application ranging from micromolecule to macromolecule detection, which can be easily extended to detect enzymes, DNA, proteins, cells, viruses, bacteria, chemicals, etc. Importantly, we found that, sensitivity was no longer subject to probe affinity when the magneto lever was sufficiently high, theoretically, even reaching single-molecule resolution.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (experimental section) is available in the online version of this article at 10.1007/s12274-022-5049-0.

Recent Advances in Nanomechanical Membrane-Type Surface Stress Sensors towards Artificial Olfaction

Nanomechanical sensors have gained significant attention as powerful tools for detecting, distinguishing, and identifying target analytes, especially odors that are composed of a complex mixture of gaseous molecules. Nanomechanical sensors and their arrays are a promising platform for artificial olfaction in combination with data processing technologies, including machine learning techniques. This paper reviews the background of nanomechanical sensors, especially conventional cantilever-type sensors. Then, we focus on one of the optimized structures for static mode operation, a nanomechanical Membrane-type Surface stress Sensor (MSS), and discuss recent advances in MSS and their applications towards artificial olfaction.

Nanomechanical sensor for rapid and ultrasensitive detection of tumor markers in serum using nanobody

Early cancer diagnosis requires ultrasensitive detection of tumor markers in blood. To this end, we develop a novel microcantilever immunosensor using nanobodies (Nbs) as receptors. As the smallest antibody (Ab) entity comprising an intact antigen-binding site, Nbs achieve dense receptor layers and short distances between antigen-binding regions and sensor surfaces, which significantly elevate the generation and transmission of surface stress. Owing to the inherent thiol group at the C-terminus, Nbs are covalently immobilized on microcantilever surfaces in directed orientation via one-step reaction, which further enhances the stress generation. For microcantilever-based nanomechanical sensor, these advantages dramatically increase the sensor sensitivity. Thus, Nb-functionalized microcantilevers can detect picomolar concentrations of tumor markers with three orders of magnitude higher sensitivity, when compared with conventional Ab-functionalized microcantilevers. This proof-of-concept study demonstrates an ultrasensitive, label-free, rapid, and low-cost method for tumor marker detection. Moreover, interestingly, we find Nb inactivation on sensor interfaces when using macromolecule blocking reagents. The adsorption-induced inactivation is presumably caused by the change of interfacial properties, due to binding site occlusion upon complex coimmobilization formations. Our findings are generalized to any coimmobilization methodology for Nbs and, thus, for the construction of high-performance immuno-surfaces.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material (experimental section, HER2 detection using anti-HER2-mAb-functionalized microcantilevers) is available in the online version of this article at 10.1007/s12274-021-3588-4.

Label-free anti-Müllerian hormone sensor based on polyaniline micellar modified electrode

A label-free electrochemical immunosensor based on polyaniline (PANI) micellar electrode was firstly fabricated for direct AMH detection. To control the size regularity of PANI, a micelle-based method using ammonium peroxydisulfate (APS) as a reducing agent was employed in the polymerization process. The Anti-AMH antibodies were readily immobilized onto PANI via peptide bond to enhance the sensor specificity and sensitivity. This sensor was applied for the detection of AMH, an ovarian response indicator in female related to residual eggs during a woman's monthly cycle. The sensor performances were systematically investigated by differential pulse voltammetry. The anodic peak current decreases with the increase of AMH concentration owing to blocking of electron transfer by AMH. Under the optimal conditions, this sensor offers high sensitivity with a low detection limit of 0.1 ng mL^-1 and a wide linear range of 0.1-4 ng mL^-1, which is sensitive enough to indicate the ability to produce eggs during a woman's monthly cycle. Furthermore, this system requires lower sample volume (5 μL), while offers the simple fabrication with low cost and no synthetic challenge and faster analysis compared with a standard ELISA. Ultimately, this sensor was successfully applied for the detection of AMH in human serum with satisfactory results. Thus, it might be an alternative tool for AMH screening in clinical setting.

Nanobodies: The "Magic Bullets" in therapeutics, drug delivery and diagnostics

Antibodies represent a well-established class of clinical diagnostics for medical applications as well as essential research and biotechnological tools. Although both polyclonal and monoclonal antibodies are indispensable reagents in basic research and diagnostics but both of them have their limitations. Hence, there is urgent need to develop strategies aimed at production of alternative scaffolds and recombinant antibodies of smaller dimensions that could be easily produced, selected and manipulated. Unlike conventional antibodies, members of Camelidae and sharks produce antibodies composed only of heavy chains with small size, high solubility, thermal stability, refolding capacity and good tissue penetration in vivo. The discovery of these naturally occurring antibodies having only heavy-chain in Camelidae family and their further development into small recombinant nanobodies represents an attractive alternative in drug delivery, diagnostics and imaging. Nanobody derivatives are soluble, stable, versatile, have unique refolding capacities, reduced aggregation tendencies and high-target binding capabilities. They can be genetically customized to target enzymes, transmembrane proteins or molecular interactions. Their ability to recognize recessed antigenic sites has been attributed to their smaller size and the ability of the extended CDR3 loop to quickly penetrate into such epitopes. With the advent of molecular engineering and phage display technology, they can be of potential use in molecular imaging, drug delivery and therapeutics for several major diseases. In this review we present the recent advances in nanobodies for modulating immune functions, for targeting cancers, viruses, toxins and microbes as well as their utility as diagnostic and biosensor tools.

Biosensors Based on Mechanical and Electrical Detection Techniques

Biosensors are powerful analytical tools for biology and biomedicine, with applications ranging from drug discovery to medical diagnostics, food safety, and agricultural and environmental monitoring. Typically, biological recognition receptors, such as enzymes, antibodies, and nucleic acids, are immobilized on a surface, and used to interact with one or more specific analytes to produce a physical or chemical change, which can be captured and converted to an optical or electrical signal by a transducer. However, many existing biosensing methods rely on chemical, electrochemical and optical methods of identification and detection of specific targets, and are often: complex, expensive, time consuming, suffer from a lack of portability, or may require centralised testing by qualified personnel. Given the general dependence of most optical and electrochemical techniques on labelling molecules, this review will instead focus on mechanical and electrical detection techniques that can provide information on a broad range of species without the requirement of labelling. These techniques are often able to provide data in real time, with good temporal sensitivity. This review will cover the advances in the development of mechanical and electrical biosensors, highlighting the challenges and opportunities therein.

Label-free, chronological and selective detection of aggregation and fibrillization of amyloid β protein in serum by microcantilever sensor immobilizing cholesterol-incorporated liposome

To facilitate the early diagnosis of Alzheimer's disease and mild cognitive impairment patients, we developed a cantilever-based microsensor that immobilized liposomes of various phospholipids to detect a trace amount of amyloid β (Aβ) protein, and investigated its aggregation and fibrillization on model cell membranes in human serum. Three species of liposomes composed of different phospholipids of 1,2-dipalmtoyl-sn-glycero-3-phosphocholine (DPPC), DPPC/phosphatidyl ethanolamine and 1,2-dipalmitoyl-sn-glycero-3-phosphorylglycerol having varied hydrophilic groups were applied, which showed different chronological interactions with Aβ(1-40) protein and varied sensitivities of the cantilever sensor, depending on their specific electrostatic charged conditions, hydrophilicity, and membrane fluidity. 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) having short hydrophobic carbon chains confirmed to show a large interaction with Aβ(1-40) and a high sensitivity. Furthermore, the incorporation of cholesterol into DMPC was effective to selectively detect Aβ(1-40) in human serum, which effect was also checked by quartz crystal microbalance. Finally, Aβ detection of 100-pM order was expected selectively in the serum by using the developed biosensor.

Screen printed electrode-based biosensor functionalized with magnetic cobalt/single-chain antibody fragments for cocaine biosensing in different matrices

On-site detection of substance abuse is an important approach in the preventive and intervention protocols implementations. It is known that the traditional methods are heavy, time-consuming, and need a high level of logistical requirements. As such, biosensors represent great potential to simplify and improve substance abuse detection. In this study, we have designed a functionalized screen-printed electrode (SPE) electrochemical biosensor with cobalt oxide nanoparticles and single-chain antibody fragments (scFvs) for cocaine detection. Different electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectrometry were used to examine the functionality of the designed biosensor. Furthermore, SEM observations were performed to observe the surface changes after functionalization. The results showed that the linearity ranged between 5.0 and 250 ng/mL and a detection limit of 3.6 ng/mL (n = 6). These results were compared to results obtained from Q-TOF/MS where four different matrices (serum, sweat, urine, and saliva) were spiked with 100 ng/mL cocaine and were analyzed by both methods (Biosensor and Q-TOF/MS). Results showed a higher performance of the biosensor compared to traditional methods. In addition, the selectivity of the biosensor was shown in the presence of different interferents where the designed platform showed a specific response to only cocaine. In conclusion, the designed biosensor proposes great potential for portable and on-site substance abuse detection in addition to boasting the capability of reuse of the SPE and thus, reducing the costs related to such applications.

Highly Sensitive Biosensors Based on Biomolecules and Functional Nanomaterials Depending on the Types of Nanomaterials: A Perspective Review

Biosensors are very important for detecting target molecules with high accuracy, selectivity, and signal-to-noise ratio. Biosensors developed using biomolecules such as enzymes or nucleic acids which were used as the probes for detecting the target molecules were studied widely due to their advantages. For example, enzymes can react with certain molecules rapidly and selectively, and nucleic acids can bind to their complementary sequences delicately in nanoscale. In addition, biomolecules can be immobilized and conjugated with other materials by surface modification through the recombination or introduction of chemical linkers. However, these biosensors have some essential limitations because of instability and low signal strength derived from the detector biomolecules. Functional nanomaterials offer a solution to overcome these limitations of biomolecules by hybridization with or replacing the biomolecules. Functional nanomaterials can give advantages for developing biosensors including the increment of electrochemical signals, retention of activity of biomolecules for a long-term period, and extension of investigating tools by using its unique plasmonic and optical properties. Up to now, various nanomaterials were synthesized and reported, from widely used gold nanoparticles to novel nanomaterials that are either carbon-based or transition-metal dichalcogenide (TMD)-based. These nanomaterials were utilized either by themselves or by hybridization with other nanomaterials to develop highly sensitive biosensors. In this review, highly sensitive biosensors developed from excellent novel nanomaterials are discussed through a selective overview of recently reported researches. We also suggest creative breakthroughs for the development of next-generation biosensors using the novel nanomaterials for detecting harmful target molecules with high sensitivity.

Simple strategy for single-chain fragment antibody-conjugated probe construction

AIMS

A combination of biomarker and instrument technology diagnosis methods, especially antigen-targeted imaging methods, is required to increase the accuracy of the diagnosis of cancer. Currently, the targeting efficiency is limited by the conjugation methods used for the conjugation of antibodies and imaging materials. Here, a simple strategy for the conjugation of a probe and a single-chain fragment antibody (scFv) that does not change the characteristics of the antibody was shown.

MAIN METHODS

An ScFv was conjugated with superparamagnetic iron oxide (SPIO) or indocyanine green (ICG) via a linker by utilizing the reaction between cysteine and maleimide. The characterization of the probe was performed by flow cytometry, confocal imaging, optical imaging and magnetic resonance imaging (MRI).

KEY FINDINGS

After conjugation, the scFv retained high affinity, antigen specificity, and strong internalization ability. The application of the conjugated probe was also confirmed by optical imaging and MRI.

SIGNIFICANCE

The proposed strategy provides a simple method for the production of high efficiency antigen-targeted imaging probes for tumor diagnosis.

Flow force augmented 3D suspended polymeric microfluidic (SPMF3 ) platform

Detection and study of bioelements using microfluidic systems has been of great interest in the biodiagnostics field. Microcantilevers are the most used systems in biodetection due to their implementation simplicity which have been used for a wide variety of applications ranging from cellular to molecular diagnosis. However, increasing further the sensitivity of the microcantilever systems have a great effect on the cantilever based sensing for chemical and bio applications. In order to improve further the performance of microcantilevers, a flow force augmented 3D suspended microchannel is proposed using which microparticles can be conveyed through a microchannel inside the microcantilever to the detection area. This innovative microchannel design addresses the low sensitivity issue by increasing its sensitivity up to 5 times than the earlier reported similar microsystems. Moreover, fabricating this microsystem out of Polydimethylsiloxane (PDMS) would eliminate external exciter dependency in many detection applications such as biodiagnostics. In this study, the designed microsystem has been analyzed theoretically, simulated and tested. Moreover, the microsystem has been fabricated and tested under different conditions, the results of which have been compared with simulation results. Finally, its innovative fabrication process and issues are reported and discussed.

Multifluorophore DNA Origami Beacon as a Biosensing Platform

Biosensors play increasingly important roles in many fields, from clinical diagnosis to environmental monitoring, and there is a growing need for cheap and simple analytical devices. DNA nanotechnology provides methods for the creation of sophisticated biosensors, however many of the developed DNA-based sensors are limited by cumbersome and time-consuming readouts involving advanced experimental techniques. Here we describe design, construction, and characterization of an optical DNA origami nanobiosensor device exploiting arrays of precisely positioned organic fluorophores. Two arrays of donor and acceptor fluorophores make up a multifluorophore Förster resonance energy-transfer pair that results in a high-output signal for microscopic detection of single devices. Arrangement of fluorophores into arrays increases the signal-to-noise ratio, allowing detection of signal output from singular biosensors using a conventional fluorescence microscopy setup. Single device analysis enables detection of target DNA sequences in concentrations down to 100 pM in <45 min. We expect that the presented nanobiosensor can function as a general platform for incorporating sensor modules for a variety of targets and that the strong signal amplification properties may allow detection in portable microscope systems to be used for biosensor applications in the field.

Epitope Binning Assay Using an Electron Transfer-Modulated Aptamer Sensor

Surface plasmon resonance and quartz crystal microbalance are workhorses of protein-DNA interaction research for over 20 years, providing ways to quantitatively determine the protein-DNA binding. However, the cost, necessary technical expertise, and severe nonspecific adsorption poses barriers to their use. Convenient and effective techniques for the measurement of protein-DNA binding affinity and the epitope binning between DNA and proteins for developing highly sensitive detection platform remain challenging. Here, we develop a binding-induced alteration in electron transfer kinetics of the redox reporter labeled (methylene blue) on DNA aptamer to measure the binding affinity between prostate-specific antigen (PSA) and aptamer. We demonstrate that the binding of PSA to aptamer decreases the electron transfer rate of methylene blue for ∼45%. Further, we identify the best pairwise selection of aptamers for developing sandwich assay by sorting from 10 pairwise modes with the PSA detection limit of 500 ng/mL. Our study provides promising ways to analyze the binding affinity between ligand and receptor and to sort pairwise between aptamers or antibodies for the development of highly sensitive sandwich immunoassays.

Optical-Interferometry-Based CMOS-MEMS Sensor Transduced by Stress-Induced Nanomechanical Deflection

We developed a Fabry-Perot interferometer sensor with a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for chemical sensing. The novel signal transducing technique was performed in three steps: mechanical deflection, transmittance change, and photocurrent change. A small readout photocurrent was processed by an integrated source follower circuit. The movable film of the sensor was a 350-nm-thick polychloro-para-xylylene membrane with a diameter of 100 µm and an air gap of 300 nm. The linearity of the integrated source follower circuit was obtained. We demonstrated a gas response using 80-ppm ethanol detected by small membrane deformation of 50 nm, which resulted in an output-voltage change with the proposed high-efficiency transduction.

Nano-Integrated Suspended Polymeric Microfluidics (SPMF) Platform for Ultra-Sensitive Bio-Molecular Recognition of Bovine Growth Hormones

The development of sensitive platforms for the detection of biomolecules recognition is an extremely important problem in clinical diagnostics. In microcantilever (MC) transducers, surface-stress is induced upon bimolecular interaction which is translated into MC deflection. This paper presents a cost-effective and ultra-sensitive MC-based biosensing platform. To address these goals, the need for costly high-resolution read-out system has been eliminated by reducing the cantilever compliance through developing a polymer-based cantilever. Furthermore a microfluidic system has been integrated with the MC in order to enhance sensitivity and response time and to reduce analytes consumption. Gold nanoparticles (AuNPs) are synthesized on the surface of suspended microfluidics as the selective layer for biomolecule immobilization. The biosensing results show significant improvement in the sensitivity of the proposed platform compared with available silicon MC biosensor. A detection limit of 2 ng/ml (100pM) is obtained for the detection of bovine growth hormones. The results validated successful application of suspended polymeric microfluidics (SPMF) as the next generation of biosensing platforms which could enable femtomolar (fM) biomolecular recognition detection.

Fast Diagnostics of BRAF Mutations in Biopsies from Malignant Melanoma

According to the American skin cancer foundation, there are more new cases of skin cancer than the combined incidence of cancers of the breast, prostate, lung, and colon each year, and malignant melanoma represents its deadliest form. About 50% of all cases are characterized by a particular mutation BRAF(V600E) in the BRAF (Rapid Acceleration of Fibrosarcoma gene B) gene. Recently developed highly specific drugs are able to fight BRAF(V600E) mutated tumors but require diagnostic tools for fast and reliable mutation detection to warrant treatment efficiency. We completed a preliminary clinical trial applying cantilever array sensors to demonstrate identification of a BRAF(V600E) single-point mutation using total RNA obtained from biopsies of metastatic melanoma of diverse sources (surgical material either frozen or fixated with formalin and embedded in paraffin). The method is faster than the standard Sanger or pyrosequencing methods and comparably sensitive as next-generation sequencing. Processing time from biopsy to diagnosis is below 1 day and does not require PCR amplification, sequencing, and labels.

Microfluidic-Based Multi-Organ Platforms for Drug Discovery

Development of predictive multi-organ models before implementing costly clinical trials is central for screening the toxicity, efficacy, and side effects of new therapeutic agents. Despite significant efforts that have been recently made to develop biomimetic in vitro tissue models, the clinical application of such platforms is still far from reality. Recent advances in physiologically-based pharmacokinetic and pharmacodynamic (PBPK-PD) modeling, micro- and nanotechnology, and in silico modeling have enabled single- and multi-organ platforms for investigation of new chemical agents and tissue-tissue interactions. This review provides an overview of the principles of designing microfluidic-based organ-on-chip models for drug testing and highlights current state-of-the-art in developing predictive multi-organ models for studying the cross-talk of interconnected organs. We further discuss the challenges associated with establishing a predictive body-on-chip (BOC) model such as the scaling, cell types, the common medium, and principles of the study design for characterizing the interaction of drugs with multiple targets.

Microfluidics in the selection of affinity reagents for the detection of cancer: paving a way towards future diagnostics

Microfluidic technologies have miniaturized a variety of biomedical applications, and these chip-based systems have several significant advantages over their large-scale counterparts. Recently, this technology has been used for automating labor-intensive and time-consuming screening processes, whereby affinity reagents, including aptamers, peptides, antibodies, polysaccharides, glycoproteins, and a variety of small molecules, are used to probe for molecular biomarkers. When compared to conventional methods, the microfluidic approaches are faster, more compact, require considerably smaller quantities of samples and reagents, and can be automated. Furthermore, they allow for more precise control of reaction conditions (e.g., pH, temperature, and shearing forces) such that more efficient screening can be performed. A variety of affinity reagents for targeting cancer cells or cancer biomarkers are now available and will likely replace conventional antibodies. In this review article, the selection of affinity reagents for cancer cells or cancer biomarkers on microfluidic platforms is reviewed with the aim of highlighting the utility of such approaches in cancer diagnostics.

Piezoresistive Membrane Surface Stress Sensors for Characterization of Breath Samples of Head and Neck Cancer Patients

For many diseases, where a particular organ is affected, chemical by-products can be found in the patient’s exhaled breath. Breath analysis is often done using gas chromatography and mass spectrometry, but interpretation of results is difficult and time-consuming. We performed characterization of patients’ exhaled breath samples by an electronic nose technique based on an array of nanomechanical membrane sensors. Each membrane is coated with a different thin polymer layer. By pumping the exhaled breath into a measurement chamber, volatile organic compounds present in patients’ breath diffuse into the polymer layers and deform the membranes by changes in surface stress. The bending of the membranes is measured piezoresistively and the signals are converted into voltages. The sensor deflection pattern allows one to characterize the condition of the patient. In a clinical pilot study, we investigated breath samples from head and neck cancer patients and healthy control persons. Evaluation using principal component analysis (PCA) allowed a clear distinction between the two groups. As head and neck cancer can be completely removed by surgery, the breath of cured patients was investigated after surgery again and the results were similar to those of the healthy control group, indicating that surgery was successful.

Highly sensitive ligand-binding assays in pre-clinical and clinical applications: immuno-PCR and other emerging techniques

Recombinant DNA technology and corresponding innovations in molecular biology, chemistry and medicine have led to novel therapeutic biomacromolecules as lead candidates in the pharmaceutical drug development pipelines. While monoclonal antibodies and other proteins provide therapeutic potential beyond the possibilities of small molecule drugs, the concomitant demand for supportive bioanalytical sample testing creates multiple novel challenges. For example, intact macromolecules can usually not be quantified by mass-spectrometry without enzymatic digestion and isotopically labeled internal standards are costly and/or difficult to prepare. Classical ELISA-type immunoassays, on the other hand, often lack the sensitivity required to obtain pharmacokinetics of low dosed drugs or pharmacodynamics of suitable biomarkers. Here we summarize emerging state-of-the-art ligand-binding assay technologies for pharmaceutical sample testing, which reveal enhanced analytical sensitivity over classical ELISA formats. We focus on immuno-PCR, which combines antibody specificity with the extremely sensitive detection of a tethered DNA marker by quantitative PCR, and alternative nucleic acid-based technologies as well as methods based on electrochemiluminescence or single-molecule counting. Using case studies, we discuss advantages and drawbacks of these methods for preclinical and clinical sample testing.

Site-specific scFv labelling with invertase via Sortase A mechanism as a platform for antibody-antigen detection using the personal glucose meter

Antibody labelling to reporter molecules is gaining popularity due to its many potential applications for diagnostics and therapeutics. However, non-directional bioconjugation methods which are commonly used often results in the loss of target binding capabilities. Therefore, a site-specific enzymatic based bioconjugation such as sortase-mediated transpeptidation allows for a more rapid and efficient method of antibody conjugation for diagnostic applications. Here we describe the utilization of sortase A bioconjugation to conjugate a single chain fragment variable (scFv) to the extracellular invertase (invB) from Zymomonas mobilis with the aim of developing an invertase based immunoassay. In addition, conjugation to enhanced green fluorescent protein (eGFP) was also validated to show the flexibility of the method. The invertase conjugated complex was successfully applied for the detection of antibody-antigen interaction using a personal glucose meter (PGM) for assay readout. The setup was used in both a direct and competitive assay highlighting the robustness of the conjugate for assay development. The method provides an alternative conjugation process to allow easy exchange of antibodies to facilitate rapid development of diagnostic assays for various diseases on the PGM platform.

Nanomechanical Sensors

This chapter introduces nanomechanical sensors and their applications. All molecules have “volume” and “mass.” Direct measurement of these fundamental parameters can realize label-free and real-time measurements. Nanomechanical sensors have been emerging as a key device for such label-free and real-time measurements with their multiple operation modes; static and dynamic modes for detecting volume- and mass-related features, respectively. A cantilever array sensor is a representative example among various geometries, while structural optimization can enhance the scope of nanomechanical sensors in both academic and industrial applications. One of the most advanced sensing platforms is a membrane-type surface stress sensor (MSS), which realizes both high sensitivity and compact system at the same time. The MSS is also expected to contribute to addressing nanomechanical behavior of living cells and their network.

Asymmetric immobilization of antibodies on a piezo-resistive micro-cantilever surface

For cantilever-based MEMS sensors, selective chemical modification of the sensing surface is used for the detection of chemical and biological analytes.

Decoupling competing surface binding kinetics and reconfiguration of receptor footprint for ultrasensitive stress assays

Cantilever arrays have been used to monitor biochemical interactions and their associated stress. However, it is often necessary to passivate the underside of the cantilever to prevent unwanted ligand adsorption, and this process requires tedious optimization. Here, we show a way to immobilize membrane receptors on nanomechanical cantilevers so that they can function without passivating the underlying surface. Using equilibrium theory, we quantitatively describe the mechanical responses of vancomycin, human immunodeficiency virus type 1 antigens and coagulation factor VIII captured on the cantilever in the presence of competing stresses from the top and bottom cantilever surfaces. We show that the area per receptor molecule on the cantilever surface influences ligand-receptor binding and plays an important role on stress. Our results offer a new way to sense biomolecules and will aid in the creation of ultrasensitive biosensors.

Corallite-like Magnetic Fe3O4@MnO2@Pt Nanocomposites as Multiple Signal Amplifiers for the Detection of Carcinoembryonic Antigen

A nonenzymatic sandwich-type electrochemical immunosensor using corallite-like magnetic Fe3O4@MnO2@Pt nanocomposites was developed for the sensitive detection of carcinoembryonic antigen (CEA). First, aminated graphene (GS-NH2) sheets were synthesized from graphite oxide using the Hummers' method, which was used to immobilize the primary antibody via the active amino groups on the GS-NH2. Second, corallite-like Fe3O4@MnO2@Pt nanoparticles (NPs) were synthesized and characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). They were used as labels to conjugate with a secondary antibody. The multiple amplification of Fe3O4@MnO2@Pt NPs and the promoted electron transfer of GS-NH2 lead to a broad linear range from 0.5 pg/mL to 20 ng/mL and a low detection limit with 0.16 pg/mL. In addition, the immunosensor performed with good selectivity and acceptable stability and reproducibility as well. The results are satisfactory when the proposed method has been applied to analyze human serum samples. Thus, there would be a promising future in the early diagnosis of cancer to detect CEA and other tumor markers.

A Micro-Preconcentrator Combined Olfactory Sensing System with a Micromechanical Cantilever Sensor for Detecting 2,4-Dinitrotoluene Gas Vapor

Preventing unexpected explosive attacks and tracing explosion-related molecules require the development of highly sensitive gas-vapor detection systems. For that purpose, a micromechanical cantilever-based olfactory sensing system including a sample preconcentrator was developed to detect 2,4-dinitrotoluene (2,4-DNT), which is a well-known by-product of the explosive molecule trinitrotoluene (TNT) and exists in concentrations on the order of parts per billion in the atmosphere at room temperature. A peptide receptor (His-Pro-Asn-Phe-Ser-Lys-Tyr-Ile-Leu-His-Gln-Arg) that has high binding affinity for 2,4-DNT was immobilized on the surface of the cantilever sensors to detect 2,4-DNT vapor for highly selective detection. A micro-preconcentrator (µPC) was developed using Tenax-TA adsorbent to produce higher concentrations of 2,4-DNT molecules. The preconcentration was achieved via adsorption and thermal desorption phenomena occurring between target molecules and the adsorbent. The µPC directly integrated with a cantilever sensor and enhanced the sensitivity of the cantilever sensor as a pretreatment tool for the target vapor. The response was rapidly saturated within 5 min and sustained for more than 10 min when the concentrated vapor was introduced. By calculating preconcentration factor values, we verified that the cantilever sensor provides up to an eightfold improvement in sensing performance.

Mechanochemical Sensing: A Biomimetic Sensing Strategy

Existing biosensors employ two major components: analyte recognition and signal transduction. Although specificity is achieved through analyte recognition, sensitivity is usually enhanced through a chemical amplification stage that couples the two main units in a sensor. Although highly sensitive, the extra chemical amplification stage complicates the sensing protocol. In addition, it separates the two elements spatiotemporally, reducing the real-time response of the biosensor. In this review, we discuss the new mechanochemical biosensors that employ mechanochemical coupling strategies to overcome these issues. By monitoring changes in the mechanical properties of a single-molecule template upon analyte binding, single-molecule sensitivity is reached. As chemical amplification becomes unnecessary in this single-molecule mechanochemical sensing (SMMS) strategy, real-time sensing is achieved.

Using surface enhanced Raman scattering to analyze the interactions of protein receptors with bacterial quorum sensing modulators

Many members of the LuxR family of quorum sensing (QS) transcriptional activators, including LasR of Pseudomonas aeruginosa, are believed to require appropriate acyl-homoserine lactone (acyl-HSL) ligands to fold into an active conformation. The failure to purify ligand-free LuxR homologues in nonaggregated form at the high concentrations required for their structural characterization has limited the understanding of the mechanisms by which QS receptors are activated. Surface-enhanced Raman scattering (SERS) is a vibrational spectroscopy technique that can be applied to study proteins at extremely low concentrations in their active state. The high sensitivity of SERS has allowed us to detect molecular interactions between the ligand-binding domain of LasR (LasRLBD) as a soluble apoprotein and modulators of P. aeruginosa QS. We found that QS activators and inhibitors produce differential SERS fingerprints in LasRLBD, and in combination with molecular docking analysis provide insight into the relevant interaction mechanism. This study reveals signal-specific structural changes in LasR upon ligand binding, thereby confirming the applicability of SERS to analyze ligand-induced conformational changes in proteins.

Miniaturization of multiplexed planar recombinant antibody arrays for serum protein profiling

BACKGROUND

Antibody-based microarrays are a developing tool for high-throughput proteomics in health and disease. However, in order to enable global proteome profiling, novel miniaturized high-density antibody array formats must be developed.

RESULTS

In this proof-of-concept study, we have designed a miniaturized planar recombinant (single-chain Fragment variable). antibody array technology platform for multiplexed profiling of non-fractionated, directly labelled serum samples. The size of the individual spot features was reduced 225-times (78.5 μm(2)/spot) and the array density was increased 19-times (38,000 spots/cm(2)). These miniaturized, multiplexed arrays were produced, using a desktop nanofabrication system based on dip-pen nanolithography technology, and interfaced with a high-resolution fluorescent-based scanner. The reproducibility, sensitivity, specificity, and applicability of the set-up were demonstrated by profiling a set of well-characterized serum samples.

CONCLUSION

The designed antibody array platform opens up new possibilities for large-scale, multiplex profiling of crude proteomes in a miniaturized fashion.

Fabrication of plasmon length-based surface enhanced Raman scattering for multiplex detection on microfluidic device

The length of bioreceptors plays an important role in signal enhancement of surface-enhanced Raman scattering (SERS) due to amplification of electromagnetic fields generated by the excitation of localized surface plasmons. Herein, intact antibodies (IgG) and Fab fragments conjugated onto gold nanostar were used to fabricate two kinds of immunosensors for measurement of their SERS signals. Using CA125 as the antigen and Rhodamine-6G (R6G)-conjugated immunogolds, a SERS immunosensor was self-assembled by antigen-antibody interaction. The results showed that the SERS signal from the Fab immunosensor was 2.4 times higher than that of the IgG immunosensor. Furthermore, increased hot-spots by silver atom deposition onto the IgG and Fab immunosensor showed 2.1 and 1.4 times higher signals than before enhancement, respectively. For application, based on the Fab immunosensor, a SERS-compatible microfluidic system was designed for multiplex assays to overcome the drawbacks of conventional assays. This system can measure biological specimens directly from bio fluids instead of using a complex microfluidic device containing separation and detection elements. Four approved biomarkers of breast cancer, including cancer antigen (CA125), HER2, epididymis protein (HE4), and Eotaxin-1, were detected from patient-mimicked serum with limits of 15 fM, 17 fM, 21 fM, and 6.5 fM, respectively. The results indicated that the lengths and geometry of the bioreceptors determined the intensity of SERS signal from the interface and cavity of the sandwich immunosensor. Silver atom deposition at the cavity of the immunosensor increased the SERS signal. Finally, the SERS immunosensor built-in microfluidic system improved the performance of multiplex diagnostics.

Accurate characterization of benign and cancerous breast tissues: aspecific patient studies using piezoresistive microcantilevers

Breast cancer is the largest detected cancer amongst women in the US. In this work, our team reports on the development of piezoresistive microcantilevers (PMCs) to investigate their potential use in the accurate detection and characterization of benign and diseased breast tissues by performing indentations on the micro-scale tissue specimens. The PMCs used in these experiments have been fabricated using laboratory-made silicon-on-insulator (SOI) substrate, which significantly reduces the fabrication costs. The PMCs are 260 μm long, 35 μm wide and 2 μm thick with resistivity of order 1.316×10(-3) Ω cm obtained by using boron diffusion technique. For indenting the tissue, we utilized 8 μm thick cylindrical SU-8 tip. The PMC was calibrated against a known AFM probe. Breast tissue cores from seven different specimens were indented using PMC to identify benign and cancerous tissue cores. Furthermore, field emission scanning electron microscopy (FE-SEM) of benign and cancerous specimens showed marked differences in the tissue morphology, which further validates our observed experimental data with the PMCs. While these patient aspecific feasibility studies clearly demonstrate the ability to discriminate between benign and cancerous breast tissues, further investigation is necessary to perform automated mechano-phenotyping (classification) of breast cancer: from onset to disease progression.

Micro- and nano-structure based oligonucleotide sensors

This paper presents a review of micro- and nano-structure based oligonucleotide detection and quantification techniques. The characteristics of such devices make them very attractive for Point-of-Care or On-Site-Testing biosensing applications. Their small scale means that they can be robust and portable, their compatibility with modern CMOS electronics means that they can easily be incorporated into hand-held devices and their suitability for mass production means that, out of the different approaches to oligonucleotide detection, they are the most suitable for commercialisation. This review discusses the advantages of micro- and nano-structure based sensors and covers the various oligonucleotide detection techniques that have been developed to date. These include: Bulk Acoustic Wave and Surface Acoustic Wave devices, micro- and nano-cantilever sensors, gene Field Effect Transistors, and nanowire and nanopore based sensors. Oligonucleotide immobilisation techniques are also discussed.

Simultaneous MEMS-based electro-mechanical phenotyping of breast cancer

Carcinomas are the most commonly diagnosed cancers originating in the skin, lungs, breasts, pancreas, and other organs and glands. In most of the cases, the microenvironment within the tissue changes with the progression of disease. A key challenge is to develop a device capable of providing quantitative indicators in diagnosing cancer by measuring alteration in electrical and mechanical property of the tissues from the onset of malignancy. We demonstrate micro-electro-mechanical-systems (MEMS) based flexible polymer microsensor array capable of simultaneously measuring electro-mechanical properties of the breast tissues cores (1 mm in diameter and 10 μm in thickness) from onset through progression of the cancer. The electrical and mechanical signatures obtained from the tissue cores shows the capability of the device to clearly demarcate the specific stages of cancer in epithelial and stromal regions providing quantitative indicators facilitating the diagnosis of breast cancer. The present study shows that electro-mechanical properties of the breast tissue core at the micro-level are different than those at the macro-level.

Mechanical phenotyping of breast cancer using MEMS: a method to demarcate benign and cancerous breast tissues

The mechanical properties of tissue change significantly during the progression from healthy to malignant. Quantifying the mechanical properties of breast tissue within the tumor microenvironment can help to delineate benign from cancerous stages. In this work, we study high-grade invasive ductal carcinoma in comparison with their matched tumor adjacent areas, which exhibit benign morphology. Such paired tissue cores obtained from eight patients were indented using a MEMS-based piezoresistive microcantilever, which was positioned within pre-designated epithelial and stromal areas of the specimen. Field emission scanning electron microscopy studies on breast tissue cores were performed to understand the microstructural changes from benign to malignant. The normal epithelial tissues appeared compact and organized. The appearance of cancer regions, in comparison, not only revealed increased cellularity but also showed disorganization and increased fenestration. Using this technique, reliable discrimination between epithelial and stromal regions throughout both benign and cancerous breast tissue cores was obtained. The mechanical profiling generated using this method has the potential to be an objective, reproducible, and quantitative indicator for detecting and characterizing breast cancer.

Nanomechanical sensors for single microbial cell growth monitoring

A nanomechanical technique for rapid real time detection and monitoring of microorganism growth will significantly reduce costs and diagnosis times in industrial and clinical settings. Owing to their label free detection mechanism and unprecedented sensitivity to the mass and elastic modulus of biological structures, dynamically operated cantilever arrays provide an opportunity to rapidly detect and track the evolution of microbial growth. Here we report the monitoring of the growth of single Aspergillus niger spores via the multimode response of microcantilevers. The fungal hyphal structure affects the cantilevers' nanomechanical properties as it propagates along the sensor. We demonstrate, for the first time, the mapping of cellular events with great accuracy using a cantilever frequency response. Imaging of growth conditions on the cantilever, which is performed in parallel, allows for verification of these results. Theoretical comparison and finite element modelling confirm experimental findings and allow for determination of the hyphal elastic modulus.

Generation of miniaturized planar ecombinant antibody arrays using a microcantilever-based printer

Miniaturized (Ø 10 μm), multiplexed (>5-plex), and high-density (>100 000 spots cm(-2)) antibody arrays will play a key role in generating protein expression profiles in health and disease. However, producing such antibody arrays is challenging, and it is the type and range of available spotters which set the stage. This pilot study explored the use of a novel microspotting tool, Bioplume(TM)-consisting of an array of micromachined silicon cantilevers with integrated microfluidic channels-to produce miniaturized, multiplexed, and high-density planar recombinant antibody arrays for protein expression profiling which targets crude, directly labelled serum. The results demonstrated that 16-plex recombinant antibody arrays could be produced-based on miniaturized spot features (78.5 um(2), Ø 10 μm) at a 7-125-times increased spot density (250 000 spots cm(-2)), interfaced with a fluorescent-based read-out. This prototype platform was found to display adequate reproducibility (spot-to-spot) and an assay sensitivity in the pM range. The feasibility of the array platform for serum protein profiling was outlined.

Multiplexing of miniaturized planar antibody arrays for serum protein profiling--a biomarker discovery in SLE nephritis

In the quest to decipher disease-associated biomarkers, miniaturized and multiplexed antibody arrays may play a central role in generating protein expression profiles, or protein maps, of crude serum samples. In this conceptual study, we explored a novel, 4-times larger pen design, enabling us to, in a unique manner, simultaneously print 48 different reagents (antibodies) as individual 78.5 μm(2) (10 μm in diameter) sized spots at a density of 38,000 spots cm(-2) using dip-pen nanolithography technology. The antibody array set-up was interfaced with a high-resolution fluorescent-based scanner for sensitive sensing. The performance and applicability of this novel 48-plex recombinant antibody array platform design was demonstrated in a first clinical application targeting SLE nephritis, a severe chronic autoimmune connective tissue disorder, as the model disease. To this end, crude, directly biotinylated serum samples were targeted. The results showed that the miniaturized and multiplexed array platform displayed adequate performance, and that SLE-associated serum biomarker panels reflecting the disease process could be deciphered, outlining the use of miniaturized antibody arrays for disease proteomics and biomarker discovery.