Development of an ImmunoFET for Analysis of Tumour Necrosis Factor-α in Artificial Saliva: Application for Heart Failure Monitoring

An electrochemical immunosensor based on a nano-ceria integrated microfluidic chip for interleukin-8 biomarker detection

Interleukin-8 (IL8) is an important cytokine that plays a significant role in tumor growth and angiogenesis across various malignant tumors, including oral squamous cell carcinoma (OSCC). It is an important biomarker for oral cancer; therefore, its early and accurate detection in bodily fluid reduces morbidity and mortality rates in cancer patients. The work presents the development of a label-free microfluidic miniaturized electrochemical immunosensor for IL8 biomarker detection at low concentration in saliva samples. A rapid, sensitive and selective biosensing platform was developed for IL8 detection using a nano-ceria integrated microfluidic system. The synthesized nano-ceria particles (8.13 nm) were employed to enhance the electrochemical biosensing signal and sensitivity of the biosensor due to their high catalytic properties and large surface area. For this, microfluidic chip was prepared by Indium tin oxide (ITO) (3 × 4 cm) containing three electrode patterns of working, reference and counter electrode. These electrode patterns were developed using a maskless photolithography technique and a polydimethylsiloxane (PDMS) mold created a 200 μm wide microchannel which was bound to the susbtrate using plasma treatment. Spectroscopy and microscopy techniques were used to confirm the synthesis of nano-ceria. Furthermore, electrode surface modifications were achieved by immobilization of chemically activated antibodies of IL8, as verified by Fourier transform-infrared spectroscopy (FT-IR). Furthermore, differential pulse voltammetry (DPV) was utilized to investigate electrochemical parameters and conduct biosensing studies. The developed electrochemical microfluidic biosensing platform works for an IL8 antigen in the concentrations ranging from 0.004 to 10 ng mL-1 with a limit of detection (LOD) and limit of quantification (LOQ) of 0.0001 ng mL-1 and 0.0006 ng mL-1, respectively. Moreover, the developed electrochemical biosensing platform was validated using human saliva samples, achieving percentage recovery within an acceptable range.

Optimized aptamer-based next generation biosensor for the ultra-sensitive determination of SARS-CoV-2 S1 protein in saliva samples

COVID-19 is an infectious disease caused by the SARS-CoV-2 virus, which rapidly spread worldwide and resulted in a pandemic. Efficient and sensitive detection techniques have been devised since the onset of the epidemic and continue to be improved at present. Due to the crucial role of the SARS-CoV-2 S1 protein in facilitating the virus's entry into cells, efforts in detection and treatment have primarily centered upon this protein. In this study, a rapid, ultrasensitive, disposable, easy-to-use, cost-effective next generation biosensor based on optimized aptamer (Optimer, OPT) was developed by using a disposable pencil graphite electrode (PGE) and applied for the impedimetric determination of SARS-CoV-2 S1 protein. The S1 protein interacted with the OPT in the solution phase and then immobilized onto the PGE surface. Subsequently, measurements using electrochemical impedance spectroscopy (EIS) were conducted in a solution containing a redox probe of 1 mM [Fe(CN)6]3-/4-. Under optimum conditions, the limit of detection (LOD) for the S1 protein in buffer medium at concentrations ranging from 101 to 106 ag/mL was calculated as 8.80 ag/mL (0.11 aM). The selectivity of the developed biosensor was studied against MERS-CoV-S1 protein (MERS) and Influenza Hemagglutinin antigen (HA). Furthermore, the application of the biosensor in artificial saliva medium is demonstrated. The LOD was also calculated in artificial saliva medium in the concentration range of 101-105 ag/mL and calculated as 2.01 ag/mL (0.025 aM). This medium was also used to assess the selectivity of optimized-aptamer based biosensor.

A bioinspired porous and electroactive reduced graphene oxide hydrogel based biosensing platform for efficient detection of tumor necrosis factor-α

Oral cancer is one of the leading cancer types, which is frequently diagnosed at an advanced stage, giving patients a poor prognosis and fewer therapeutic choices. To address this gap, exploiting biosensors utilizing anti-biofouling hydrogels for early-stage oral cancer detection in non-invasive body fluids is gaining utter importance. Herein, we have demonstrated the fabrication of an innovative electrochemical immunosensor for the rapid, label-free, non-invasive, and affordable detection of tumor necrosis factor-α (TNF-α), a biomarker associated with oral cancer progression in artificial saliva samples. The gold screen-printed electrodes (gSPEs) are modified with a green synthesized porous and electroactive reduced graphene oxide (rGO) hydrogel utilizing L-cystine (L-cys) as both in situ reducing and surface functionalization agent, followed by covalent immobilization of anti-TNF-α and blocking of residual sites with bovine serum albumin (BSA) to fabricate the BSA/anti-TNF-α/L-cys_rGO hydrogel/gSPE immunosensing platform. The fabricated platform demonstrates excellent performance, with a low limit of detection of 1.20 pg mL-1, a broad linear range from 1 to 200 pg mL-1, and a high sensitivity of 2.10 μA pg-1 mL cm-2 carried out with differential pulse voltammetry (DPV) technique. Moreover, it exhibits specificity towards TNF-α, even in the presence of potential interferents and other cancer biomarkers. Besides, the biosensor showed good reproducibility and repeatability with a relative standard deviation (%RSD) of 5.11% and 1.85%, respectively. Thus, integrating the L-cys_rGO hydrogel in the immunosensor design offers enhanced performance, paving the way for its application in early-stage oral cancer diagnosis.

Immuno field-effect transistor (ImmunoFET) for detection of salivary cortisol using potentiometric and impedance spectroscopy for monitoring heart failure

Cortisol, a steroid hormone mostly known as "the stress hormone," plays many essential functions in humans due its involvement in several metabolic pathways. It is well-known that cortisol dysregulation is implied in evolution and progression of several chronic pathologies, including cardiac diseases such as heart failure (HF). However, although several sensors have been proposed to date for the determination of cortisol, none of them has been designed for its determination in saliva in order to monitor HF progression. In this work, a silicon nitride based Immuno field-effect transistor (ImmunoFET) has been proposed to quantify salivary cortisol for HF monitoring. Sensitive biological element was represented by anti-cortisol antibody bound onto the ISFET gate via 11-triethoxysilyl undecanal (TESUD) by vapor-phase method. Potentiometric and electrochemical impedance spectroscopy (EIS) measurements were carried out for preliminary investigations on device responsiveness. Subsequently, a more sensitive detection was obtained using electrochemical EIS. The proposed device has proven to have a linear response (R² always >0.99), to be sensitive (with a limit of detection, LoD, of 0.005 ± 0.002 ng/mL), selective in case of other HF biomarkers (e.g. N-terminal pro B-type natriuretic peptide (NT-proBNP), tumor necrosis factor-alpha (TNF-α), and interleukin 10 (IL-10)), and accurate in cortisol quantification in saliva sample by performing the standard addition method.

Non-covalent π-π functionalized Gii-senseⓇ graphene foam for interleukin 10 impedimetric detection

Monitoring Interleukin 10 (IL-10) is essential for understanding the vast responses of T-cells in cancer, autoimmunity, and internal homeostasis after physical stress. However, current diagnostic methods are complex and more focused on medical screening rather than point-of-care monitoring. Biosensors based on graphene's conductivity and flexibility are attractive to offer simple single-use and reduced handling. However, oxidation of its carbon lattice to develop functional moieties for biomolecule immobilization cuts down its electronic conductivity potential. In this work, the authors present a microfluidic lab-on-chip device for simple impedimetric monitoring of IL-10 based on graphene foam (GF) flexible electrodes. Graphene's structure was maintained by employing π-π non-covalent functionalization with pyrene carboxylic acid (PCA). Impedimetric measurements could be performed in low ionic strength phosphate-buffered saline (LI-PBS). The PCA-antibody modification showed to endure the incubation, measurement, and washing processes performed in the microfluidic device. Electrode modification and measurements were characterized by, electrochemical impedance spectroscopy (EIS), contact angle, and scanning electron microscopy. From the contact angle results, we found that the wettability of the graphene surface increased gradually after each modification step. Detection measurements performed in the 3D-printed microfluidic device showed a linear response between 10 fg/mL to 100 fg/mL with a limit of detection (LOD) of 7.89 fg/mL in artificial saliva. With these features, the device was used to quantify IL-10 samples by the standard addition method for 10 fg and 50 fg with recoveries between 82% and 99%. Specificity was evaluated towards interleukin 6, TNF-⍺ and bovine serum albumin.

Selective Antibody-Free Sensing Membranes for Picogram Tetracycline Detection

As an antibody-free sensing membrane for the detection of the antibiotic tetracycline (TC), a liquid PVC membrane doped with the ion-pair tetracycline/θ-shaped anion [3,3'-Co(1,2-C2B9H11)2]- ([o-COSAN]-) was formulated and deposited on a SWCNT modified gold microelectrode. The chosen transduction technique was electrochemical impedance spectroscopy (EIS). The PVC membrane was composed of: the tetracycline/[o-COSAN]- ion-pair, a plasticizer. A detection limit of 0.3 pg/L was obtained with this membrane, using bis(2-ethylhexyl) sebacate as a plasticizer. The sensitivity of detection of tetracycline was five times higher than that of oxytetracycline and of terramycin, and 22 times higher than that of demeclocycline. A shelf-life of the prepared sensor was more than six months and was used for detection in spiked honey samples. These results open the way to having continuous monitoring sensors with a high detection capacity, are easy to clean, avoid the use of antibodies, and produce a direct measurement.

Field-Effect Capacitors Decorated with Ligand-Stabilized Gold Nanoparticles: Modeling and Experiments

Nanoparticles are recognized as highly attractive tunable materials for designing field-effect biosensors with enhanced performance. In this work, we present a theoretical model for electrolyte-insulator-semiconductor capacitors (EISCAP) decorated with ligand-stabilized charged gold nanoparticles. The charged AuNPs are taken into account as additional, nanometer-sized local gates. The capacitance-voltage (C–V) curves and constant-capacitance (ConCap) signals of the AuNP-decorated EISCAPs have been simulated. The impact of the AuNP coverage on the shift of the C–V curves and the ConCap signals was also studied experimentally on Al–p-Si–SiO₂ EISCAPs decorated with positively charged aminooctanethiol-capped AuNPs. In addition, the surface of the EISCAPs, modified with AuNPs, was characterized by scanning electron microscopy for different immobilization times of the nanoparticles.

Spatially hierarchical nano-architecture for real time detection of Interleukin-8 cancer biomarker

In the present work we have developed two hierarchical nano-architectures based electrochemical immunosensors for the detection of interleukin-8 (IL-8) cytokine tumor biomarker. A comparative study has been performed for spatial nano-architectures and their relative sensing to establish the model for real time monitoring. With the first platform, the recognition layer consisted with immobilised IL-8 on aminothiol modified gold electrodes. In the second approach, the activated multi walled carbon nanotubes (MWCNT-COOH) were added in the functionalisation process by covalent attachment between the functionalities NH₂ of aminothiol and the functionalities COOH of carbon nanotubes. The surface topology of the recognition layer has been characterised by atomic force spectroscopy (AFM) and contact angle (CA) measurements. The electrochemical response of the developed sensor was measured by electrochemical impedance spectroscopy (EIS). A side-by-side comparison showed that aminothiol/activated MWCNTs/anti-IL-8 based impedimetric immunosensor exhibits high reproducibility (The relative standard deviation (R.S.D) = 3.2%, n = 3) with high stability. The present sensor allows evaluating a lower detection limit of 0.1 pg mL^-1 with a large dynamic sensitivity range from 1 pg mL^-1to 1000 pg mL^-1 covering the entire clinical therapeutic window. The developed MWCNTs based immunosensor has been calibrated by determining IL-8 in artificial plasma and showed a selective response to IL-8 even in the interfering environment of other cytokines such as Interleukin-1 (IL-1) and Interleukin-6 (IL-6).

A readout circuit realizing electrochemical impedance spectroscopy for FET-based biosensors

Electrochemical impedance spectroscopy (EIS) is a useful approach for modeling the equivalent circuit of biosensors such as field-effect transistor (FET)-based biosensors. During the process of sensor development, laboratory potentiostats are mainly used to realize the EIS. However, those devices are normally not applicable for real use-cases outside the laboratory, so miniaturized and optimized instrumentations are needed. Various integrated circuits (IC) are available that provide EIS, but these make developed systems highly dependent on semiconductor manufacturers, including component availability. In addition, these generally do not meet the instrumentation requirements for FET-based biosensors, thus external circuitry is necessary as well. In this work, an instrumentation is presented that performs EIS between 10 Hz and 100 kHz for FET-based biosensors. The instrumentation includes the generation of the excitation signal, the configuration of the semiconductor and the readout circuit. The readout circuit consists of a transimpedance amplifier with automatic gain adjustment, filter stages, a magnitude and a phase detection circuit. Since magnitude and phase are converted to a DC signal, digitization of the results is trivial without further signal processing steps, minimizing the computational load on the microcontroller. The transmission behavior of the magnitude and phase measurement circuits shows a high linearity for sinusoidal signals. Furthermore, the overall system was tested with resistors, whereby the magnitude measurement error (1.7%) and the phase shift error (1.6°) were determined within the working range of the instrumentation. The functionality of the instrumentation is demonstrated using pH-sensitive field-effect transistors (ISFET) in various solutions.Clinical relevance- Based on the electrochemical impedance spectroscopy of FET-based biosensors such as ImmunoFETs, new point-of-care testing (POCT) devices can be developed that e.g. quantitatively detect the concentration of biomarkers with very low detection limits in body fluids. The instrumentation presented in this work can be part of new generation of diagnostic tools featuring innovative sensor technologies.

Non-Invasive Electrochemical Biosensors for TNF-α Cytokines Detection in Body Fluids

The measurement of pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-α), which is an important indicator of the inflammatory process, has received increasing attention recently because it is easy to extract from body fluid and serves as an early sign of a serious systemic inflammatory disease. Developing fast and simple detection methods to quantify the concentration of TNF-α is essential. Saliva, tears, and urine, which can easily be sampled in a non-invasive way, are considered to be important matrices for monitoring and assessing the physiological status of humans; importantly, they also provide an ideal window for monitoring the concentration of TNF-α. As a fast, accurate, inexpensive, portable, and scalable method, electrochemical biosensors are very promising for biomarker detection in matrices obtained in a non-invasive manner. This review summarises and compares the electrochemical biosensors for the detection of TNF-α in a non-invasive manner and highlights recent advances and future prospects in developing high-performance electrochemical platforms for noninvasive measurement of TNF-α.

A silicon nitride ISFET based immunosensor for tumor necrosis factor-alpha detection in saliva. A promising tool for heart failure monitoring

According to the European statistics, approximately 26 million patients worldwide suffer from heart failure (HF), and this number seems to be steadily increasing. Inflammation plays a central role in the development of HF, and the pro-inflammatory cytokine Tumor necrosis factor-α (TNF-α) represents inflammation gold-standard biomarker. Early detection plays a crucial role for the prognosis and treatment of HF. An Ion Sensitive Field Effect Transistor (ISFET) based on silicon nitride transducer and biofunctionalized with anti-TNF-α antibody for label-free detection of salivary TNF-α is proposed. Electrochemical impedance spectroscopy (EIS) was used for TNF-α detection. Our ImmunoFET offered a detection limit of 1 pg mL^-1, with an analytical reproducibility expressed by a coefficient of variance (CV) resulted < 10% for the analysis of saliva samples, and an analyte recovery of 94 ± 6%. In addition, it demonstrated high selectivity when compared to other HF biomarkers such as Inteleukin-10, N-terminal pro B-type natriuretic peptide, and Cortisol. Finally, ImmunoFET accuracy in determining the unknown concentration of TNF-α was successfully tested in saliva samples by performing standard addition method. The proposed ImmunoFET showed great promise as a complementary tool for biomedical application for HF monitoring by a non-invasive, rapid and accurate assessment of TNF-α.

Salivary Biomarkers for Diagnosis and Therapy Monitoring in Patients with Heart Failure. A Systematic Review

The aim of this study was to perform a systematic review on the potential value of saliva biomarkers in the diagnosis, management and prognosis of heart failure (HF). The correlation between saliva and plasma values of these biomarkers was also studied. PubMed was searched to collect relevant literature, i.e., case-control, cross-sectional studies that either compared the values of salivary biomarkers among healthy subjects and HF patients, or investigated their role in risk stratification and prognosis in HF patients. No randomized control trials were included. The search ended on 31st of December 2020. A total of 15 studies met the inclusion criteria. 18 salivary biomarkers were analyzed and the levels of all biomarkers studied were found to be higher in HF patients compared to controls, except for amylase, sodium, and chloride that had smaller saliva concentrations in HF patients. Natriuretic peptides are the most commonly used plasma biomarkers in the management of HF. Their saliva levels show promising results, although the correlation of saliva to plasma values is weakened in higher plasma values. In most of the publications, differences in biomarker levels between HF patients and controls were found to be statistically significant. Due to the small number of patients included, larger studies need to be conducted in order to facilitate the use of saliva biomarkers in clinical practice.