Electrical detection of C-reactive protein using a single free-standing, thermally controlled piezoresistive microcantilever for highly reproducible and accurate measurements

A cost-effective smartphone-based device for rapid C-reaction protein (CRP) detection using magnetoelastic immunosensor

C-Reaction protein (CRP) is a marker of nonspecific immunity for vital signs and wound assessment, and it can be used to diagnose infections in clinical medicine. However, measuring CRP level currently requires hospital-based instruments, high-cost reagents, and a complex process, all of which have limited its full capabilities for self-detection, a growing trend in modern medicine. In this study, we developed a novel smartphone-based device using advanced methods of magnetoelastic immunosensing to mitigate these limitations. We combined a system-on-chip (SoC) hardware architecture with smartphone apps to realize the sampling of resonance frequency shift on magnetoelastic chips, which can determine the ultra-sensitivity to mass change caused by the binding of anti-CRP antibody and CRP. Through detecting a multi-group of samples, we found that the resonance frequency shift was linearly proportional to the CRP concentration in the range from 0.1 to 100 μg mL^-1, with a sensitivity of 12.90 Hz μg^-1 mL^-1 and a detection limit of 2.349 × 10^-4 μg mL^-1. Meanwhile, compared with the large-scale instrument used in clinical settings, the performance of our device was stable and significantly more portable, rapid and cost-effective, offering excellent potential for modern home-based diagnosis.

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.

Fabrication of GQD-Electrodeposited Screen-Printed Carbon Electrodes for the Detection of the CRP Biomarker

The traditional three-electrode electrochemical system used in the development of biosensors for detecting various biomarkers of interest necessitates the use of bulk electrodes, which precludes the deployment of handheld electrochemical devices in clinical applications. Affordable screen-printed carbon electrodes (SPCEs) modified with functional interfaces are being developed to enhance the sensitivity of a compact sensing system as a whole. In this work, SPCEs were fabricated on an overhead projection (OHP) sheet in three different active areas of 2 × 2, 3 × 3, and 4 × 4 mm² using a screen printing technique, and then ∼2 nm sized graphene quantum dots (GQDs) were electrodeposited over the SPCE surface to add functionality for the detection of ultralow levels of one of the cardiac biomarkers, C-reactive protein (CRP). The proposed mediator-dependent voltammetric biosensor exhibited good sensitivity, a low detection limit, and a linear range of 2.45 μA ng^-1 mL^-1 cm^-2, 0.036 ng mL^-1, and 0.5-10 ng mL^-1, respectively. The fabricated SPCE/GQDs/anti-CRP biosensor could rapidly detect CRP in less than 25 s. The intra- and interassays were performed with five sensor strips, which showed a minimum standard deviation of 1.85 and 2.8%, respectively. The SPCE/GQDs/anti-CRP electrode was used to detect CRP concentrations in a ringer lactate solution. Thus, the developed biosensor has all of the characteristics such as rapidity, inexpensive disposable electrodes, miniaturization, and a lower detection limit needed to evolve as a point-of-care (PoC) application.

Clean-Room Lithographical Processes for the Fabrication of Graphene Biosensors

This work is on developing clean-room processes for the fabrication of electrolyte-gate graphene field-effect transistors at the wafer scale for biosensing applications. Our fabrication process overcomes two main issues: removing surface residues after graphene patterning and the dielectric passivation of metallic contacts. A graphene residue-free transfer process is achieved by using a pre-transfer, sacrificial metallic mask that protects the entire wafer except the areas around the channel, source, and drain, onto which the graphene film is transferred and later patterned. After the dissolution of the mask, clean gate electrodes are obtained. The multilayer SiO2/SiNx dielectric passivation takes advantage of the excellent adhesion of SiO2 to graphene and the substrate materials and the superior impermeability of SiNx. It hinders native nucleation centers and breaks the propagation of defects through the layers, protecting from prolonged exposition to all common solvents found in biochemistry work, contrary to commonly used polymeric passivation. Since wet etch does not allow the required level of control over the lithographic process, a reactive ion etching process using a sacrificial metallic stopping layer is developed and used for patterning the passivation layer. The process achieves devices with high reproducibility at the wafer scale.

Extended Kalman Filtering Projection Method to Reduce the 3σ Noise Value of Optical Biosensors

Optical biosensors have experienced a rapid growth over the past decade because of their high sensitivity and the fact that they are label-free. Many optical biosensors rely on tracking the change in a resonance signal or an interference pattern caused by the change in refractive index that occurs upon binding to a target biomarker. The most commonly used method for tracking such a signal is based on fitting the data with an appropriate mathematical function, such as a harmonic function or a Fano, Gaussian, or Lorentz function. However, these functions have limited fitting efficiency because of the deformation of data from noise. Here, we introduce an extended Kalman filter projection (EKFP) method to address the problem of resonance tracking and demonstrate that it improves the tolerance to noise, reduces the 3σ noise value, and lowers the limit of detection (LOD). We utilize the method to process the data of experiments for detecting the binding of C-reactive protein in a urine matrix with a chirped guided mode resonance sensor and are able to improve the LOD from 10 to 1 pg/mL. Our method reduces the 3σ noise value of this measurement compared to a simple Fano fit from 1.303 to 0.015 pixels. These results demonstrate the significant advantage of the EKFP method to resolving noisy data of optical biosensors.

Surface Acoustic Wave Sensor for C-Reactive Protein Detection

A surface acoustic wave (SAW) sensor was investigated for its application in C-reactive protein (CRP) detection. Piezoelectric lithium niobate (LiNbO₃) substrates were used to study their frequency response characteristics in a SAW sensor with a CRP sensing area. After the fabrication of the SAW sensor, the immobilization process was performed for CRP/anti-CRP interaction. The CRP/anti-CRP interaction can be detected as mass variations in the sensing area. These mass variations may produce changes in the amplitude of sensor response. It was clearly observed that a CRP concentration of 0.1 μg/mL can be detected in the proposed SAW sensor. A good fitting linear relationship between the detected insertion loss (amplitude) and the concentrations of CRP from 0.1 μg/mL to 1 mg/mL was obtained. The detected shifts in the amplitude of insertion loss in SAW sensors for different CRP concentrations may be useful in the diagnosis of risk of cardiovascular diseases.

A CMOS MEMS-based Membrane-Bridge Nanomechanical Sensor for Small Molecule Detection

Small molecule compounds are necessary to detect with high sensitivity since they may cause a strong effect on the human body even in small concentrations. But existing methods used to evaluate small molecules in blood are inconvenient, costly, time-consuming, and do not allow for portable usage. In response to these shortcomings, we introduce a complementary metal-oxide-semiconductor bio-microelectromechanical system (CMOS BioMEMS) based piezoresistive membrane-bridge (MB) sensor for detecting small molecule (phenytoin) concentrations as the demonstration. Phenytoin is one of anticonvulsant drugs licensed for the management of seizures, which has a narrow therapeutic window hence a level of concentration monitoring was needed. The MB sensor was designed to enhance the structural stability and increase the sensitivity, which its signal response increased 2-fold higher than that of the microcantilever-based sensor. The MB sensor was used to detect phenytoin in different concentrations from 5 to 100  μg/mL. The limit of detection of the sensor was 4.06 ± 0.15  μg/mL and the linear detection range was 5–100  μg/mL, which was within the therapeutic range of phenytoin concentration (10–20  μg/mL). Furthermore, the MB sensor was integrated with an on-chip thermal effect eliminating modus and a reaction tank on a compact chip carrier for disposable utilization. The required amount of sample solution was only 10  μL and the response time of the sensor was about 25  minutes. The nano-mechanical MB sensing method with thermal effect compensation is specific, sensitive, robust, affordable and well reproducible; it is, therefore, an appropriate candidate for detecting small molecules.

Electrochemical Detection of C-Reactive Protein in Human Serum Based on Self-Assembled Monolayer-Modified Interdigitated Wave-Shaped Electrode

An electrochemical capacitance immunosensor based on an interdigitated wave-shaped micro electrode array (IDWµE) for direct and label-free detection of C-reactive protein (CRP) was reported. A self-assembled monolayer (SAM) of dithiobis (succinimidyl propionate) (DTSP) was used to modify the electrode array for antibody immobilization. The SAM functionalized electrode array was characterized morphologically by atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX). The nature of gold-sulfur interactions on SAM-treated electrode array was probed by X-ray photoelectron spectroscopy (XPS). The covalent linking of anti-CRP-antibodies onto the SAM modified electrode array was characterized morphologically through AFM, and electrochemically through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The application of phosphate-buffered saline (PBS) and human serum (HS) samples containing different concentrations of CRP in the electrode array caused changes in the electrode interfacial capacitance upon CRP binding. CRP concentrations in PBS and HS were determined quantitatively by measuring the change in capacitance (ΔC) through EIS. The electrode immobilized with anti-CRP-antibodies showed an increase in ΔC with the addition of CRP concentrations over a range of 0.01-10,000 ng mL-1. The electrode showed detection limits of 0.025 ng mL-1 and 0.23 ng mL-1 (S/N = 3) in PBS and HS, respectively. The biosensor showed a good reproducibility (relative standard deviation (RSD), 1.70%), repeatability (RSD, 1.95%), and adequate selectivity in presence of interferents towards CRP detection. The sensor also exhibited a significant storage stability of 2 weeks at 4 °C in 1× PBS.

Gentamicin drug monitoring for peritonitis patients by using a CMOS-BioMEMS-based microcantilever sensor

We developed a Complementary Metal-Oxide-Semiconductor Bio-Microelectromechanical Systems (CMOS-BioMEMS) based piezoresistive microcantilever sensor for detecting gentamicin, a peritonitis therapeutic small-molecule drug. In recent years, the patient-centric concept has been emphasized. In such a trend, therapeutic drug monitoring (TDM) is especially crucial for patients with peritonitis to avoid adverse reactions from a high concentration of gentamicin in the blood. With the aid of a commercialized semiconductor manufacturing process, the microcantilever sensing platform can serve as a portable, low-cost device and offer real-time detection. With chemical surface modification and capture antibody immobilization, the sensor can detect the small-molecule (< 2 kDa) gentamicin directly. We also modified the pH value of the buffer solution and applied an external electric field to promote sensor sensitivity. Comparing the change of the signals in a non-electric field of antibody immobilization and a 60-volt electric field of antibody immobilization showed that the average signal response increased 1.8 times. In the detection of gentamicin with different concentrations of 10-200 μg/mL, the limit of detection (LOD) of the sensor was 9.44 µg/mL. Finally, the detecting result of a microrcantilever sensor was compared with the one measured by a common instrument in hospital, and the high correlation was expressed between them in gentamicin detection. The CMOS-BioMEMS-based piezoresistive microcantilever sensor has been demonstrated to have great potential as a point-of-care (POC) device for real-time drug concentration monitoring.

Label-Free Electrochemical Immunoassay for C-Reactive Protein

C-reactive protein (CRP) is one of the most expressed proteins in blood during acute phase inflammation, and its minute level increase has also been recognized for the clinical diagnosis of cardio vascular diseases. Unfortunately, the available commercial immunoassays are labour intensive, require large sample volumes, and have practical limitations, such as low stability and high production costs. Hence, we have developed a simple, cost effective, and label-free electrochemical immunoassay for the measurement of CRP in a drop of serum sample using an immunosensor strip made up of a screen printed carbon electrode (SPE) modified with anti-CRP functionalized gold nanoparticles (AuNPs). The measurement relies on the decrease of the oxidation current of the redox indicator Fe³⁺/Fe²⁺, resulting from the immunoreaction between CRP and anti-CRP. Under optimal conditions, the present immunoassay measures CRP in a linear range from 0.4–200 nM (0.047–23.6 µg mL⁻¹), with a detection limit of 0.15 nM (17 ng mL⁻¹, S/N = 3) and sensitivity of 90.7 nA nM⁻¹, in addition to a good reproducibility and storage stability. The analytical applicability of the presented immunoassay is verified by CRP measurements in human blood serum samples. This work provides the basis for a low-priced, safe, and easy-to-use point-of-care immunosensor assay to measure CRP at clinically relevant concentrations.

A Real-Time Thermal Self-Elimination Method for Static Mode Operated Freestanding Piezoresistive Microcantilever-Based Biosensors

Here, we provide a method and apparatus for real-time compensation of the thermal effect of single free-standing piezoresistive microcantilever-based biosensors. The sensor chip contained an on-chip fixed piezoresistor that served as a temperature sensor, and a multilayer microcantilever with an embedded piezoresistor served as a biomolecular sensor. This method employed the calibrated relationship between the resistance and the temperature of piezoresistors to eliminate the thermal effect on the sensor, including the temperature coefficient of resistance (TCR) and bimorph effect. From experimental results, the method was verified to reduce the signal of thermal effect from 25.6 μV/°C to 0.3 μV/°C, which was approximately two orders of magnitude less than that before the processing of the thermal elimination method. Furthermore, the proposed approach and system successfully demonstrated its effective real-time thermal self-elimination on biomolecular detection without any thermostat device to control the environmental temperature. This method realizes the miniaturization of an overall measurement system of the sensor, which can be used to develop portable medical devices and microarray analysis platforms.

Sensors and Biosensors for C-Reactive Protein, Temperature and pH, and Their Applications for Monitoring Wound Healing: A Review

Wound assessment is usually performed in hospitals or specialized labs. However, since patients spend most of their time at home, a remote real time wound monitoring would help providing a better care and improving the healing rate. This review describes the advances in sensors and biosensors for monitoring the concentration of C-reactive protein (CRP), temperature and pH in wounds. These three parameters can be used as qualitative biomarkers to assess the wound status and the effectiveness of therapy. CRP biosensors can be classified in: (a) field effect transistors, (b) optical immunosensors based on surface plasmon resonance, total internal reflection, fluorescence and chemiluminescence, (c) electrochemical sensors based on potentiometry, amperometry, and electrochemical impedance, and (d) piezoresistive sensors, such as quartz crystal microbalances and microcantilevers. The last section reports the most recent developments for wearable non-invasive temperature and pH sensors suitable for wound monitoring.

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.

Poly(3,4-ethylenedioxythiophene) Bearing Phosphorylcholine Groups for Metal-Free, Antibody-Free, and Low-Impedance Biosensors Specific for C-Reactive Protein

Conducting polymers possessing biorecognition elements are essential for developing electrical biosensors sensitive and specific to clinically relevant biomolecules. We developed a new 3,4-ethylenedioxythiophene (EDOT) derivative bearing a zwitterionic phosphorylcholine group via a facile synthesis through the Michael-type addition thiol-ene "click" reaction for the detection of an acute-phase biomarker human C-reactive protein (CRP). The phosphorylcholine group, a major headgroup in phospholipid, which is the main constituent of plasma membrane, was also expected to resist nonspecific adsorption of other proteins at the electrode/solution interface. The biomimetic EDOT derivative was randomly copolymerized with EDOT, via an electropolymerization technique with a dopant sodium perchlorate, onto a glassy carbon electrode to make the synthesized polymer film both conductive and target-responsive. The conducting copolymer films were characterized by cyclic voltammetry, scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The specific interaction of CRP with phosphorylcholine in a calcium-containing buffer solution was determined by differential pulse voltammetry, which measures the altered redox reaction between the indicators ferricyanide/ferrocyanide as a result of the binding event. The conducting polymer-based protein sensor achieved a limit of detection of 37 nM with a dynamic range of 10-160 nM, covering the dynamically changing CRP levels in circulation during the acute phase. The results will enable the development of metal-free, antibody-free, and low-impedance electrochemical biosensors for the screening of nonspecific biomarkers of inflammation and infection.

Direct determination of a small-molecule drug, valproic Acid, by an electrically-detected microcantilever biosensor for personalized diagnostics

Direct, small-molecule determination of the antiepileptic drug, valproic acid, was investigated by a label-free, nanomechanical biosensor. Valproic acid has long been used as an antiepileptic medication, which is administered through therapeutic drug monitoring and has a narrow therapeutic dosage range of 50-100 μg·mL-1 in blood or serum. Unlike labeled and clinically-used measurement techniques, the label-free, electrical detection microcantilever biosensor can be miniaturized and simplified for use in portable or hand-held point-of-care platforms or personal diagnostic tools. A micromachined microcantilever sensor was packaged into the micro-channel of a fluidic system. The measurement of the antiepileptic drug, valproic acid, in phosphate-buffered saline and serum used a single free-standing, piezoresistive microcantilever biosensor in a thermally-controlled system. The measured surface stresses showed a profile over a concentration range of 50-500 μg·mL-1, which covered the clinically therapeutic range of 50-100 μg·mL-1. The estimated limit of detection (LOD) was calculated to be 45 μg·mL-1, and the binding affinity between the drug and the antibody was measured at around 90 ± 21 μg·mL-1. Lastly, the results of the proposed device showed a similar profile in valproic acid drug detection with those of the clinically-used fluorescence polarization immunoassay.

Detection of the inflammation biomarker C-reactive protein in serum samples: towards an optimal biosensor formula

The development of an electrochemical immunosensor for the biomarker, C-reactive protein (CRP), is reported in this work. CRP has been used to assess inflammation and is also used in a multi-biomarker system as a predictive biomarker for cardiovascular disease risk. A gold-based working electrode sensor was developed, and the types of electrode printing inks and ink curing techniques were then optimized. The electrodes with the best performance parameters were then employed for the construction of an immunosensor for CRP by immobilizing anti-human CRP antibody on the working electrode surface. A sandwich enzyme-linked immunosorbent assay (ELISA) was then constructed after sample addition by using anti-human CRP antibody labelled with horseradish peroxidase (HRP). The signal was generated by the addition of a mediator/substrate system comprised of 3,3,5',5'-Tetramethylbenzidine dihydrochloride (TMB) and hydrogen peroxide (H2O2). Measurements were conducted using chronoamperometry at -200 mV against an integrated Ag/AgCl reference electrode. A CRP limit of detection (LOD) of 2.2 ng·mL(-1) was achieved in spiked serum samples, and performance agreement was obtained with reference to a commercial ELISA kit. The developed CRP immunosensor was able to detect a diagnostically relevant range of the biomarker in serum without the need for signal amplification using nanoparticles, paving the way for future development on a cardiac panel electrochemical point-of-care diagnostic device.

First-principles surface stress calculations and multiscale deformation analysis of a self-assembled monolayer adsorbed on a micro-cantilever

Micro-cantilever sensors are widely used to detect biomolecules, chemical gases, and ionic species. However, the theoretical descriptions and predictive modeling of these devices are not well developed, and lag behind advances in fabrication and applications. In this paper, we present a novel multiscale simulation framework for nanomechanical sensors. This framework, combining density functional theory (DFT) calculations and finite element method (FEM) analysis, is capable of analyzing molecular adsorption-induced deformation and stress fields in the sensors from the molecular scale to the device scale. Adsorption of alkanethiolate self-assembled monolayer (SAM) on the Au(111) surface of the micro-cantilever sensor is studied in detail to demonstrate the applicability of this framework. DFT calculations are employed to investigate the molecular adsorption-induced surface stress upon the gold surface. The 3D shell elements with initial stresses obtained from the DFT calculations serve as SAM domains in the adsorption layer, while FEM is employed to analyze the deformation and stress of the sensor devices. We find that the micro-cantilever tip deflection has a linear relationship with the coverage of the SAM domains. With full coverage, the tip deflection decreases as the molecular chain length increases. The multiscale simulation framework provides a quantitative analysis of the displacement and stress fields, and can be used to predict the response of nanomechanical sensors subjected to complex molecular adsorption.

Hybrid integrated label-free chemical and biological sensors

Label-free sensors based on electrical, mechanical and optical transduction methods have potential applications in numerous areas of society, ranging from healthcare to environmental monitoring. Initial research in the field focused on the development and optimization of various sensor platforms fabricated from a single material system, such as fiber-based optical sensors and silicon nanowire-based electrical sensors. However, more recent research efforts have explored designing sensors fabricated from multiple materials. For example, synthetic materials and/or biomaterials can also be added to the sensor to improve its response toward analytes of interest. By leveraging the properties of the different material systems, these hybrid sensing devices can have significantly improved performance over their single-material counterparts (better sensitivity, specificity, signal to noise, and/or detection limits). This review will briefly discuss some of the methods for creating these multi-material sensor platforms and the advances enabled by this design approach.