Non-Faradaic electrical impedimetric investigation of the interfacial effects of neuronal cell growth and differentiation on silicon nanowire transistors

Noninvasive and Continuous Monitoring of On-Chip Stem Cell Osteogenesis Using a Reusable Electrochemical Immunobiosensor

Noninvasive monitoring of biofabricated tissues during the biomanufacturing process is needed to obtain reproducible, healthy, and functional tissues. Measuring the levels of biomarkers secreted from tissues is a promising strategy to understand the status of tissues during biofabrication. Continuous and real-time information from cultivated tissues enables users to achieve scalable manufacturing. Label-free biosensors are promising candidates for detecting cell secretomes since they can be noninvasive and do not require labor-intensive processes such as cell lysing. Moreover, most conventional monitoring techniques are single-use, conducted at the end of the fabrication process, and, challengingly, are not permissive to in-line and continual detection. To address these challenges, we developed a noninvasive and continual monitoring platform to evaluate the status of cells during the biofabrication process, with a particular focus on monitoring the transient processes that stem cells go through during in vitro differentiation over extended periods. We designed and evaluated a reusable electrochemical immunosensor with the capacity for detecting trace amounts of secreted osteogenic markers, such as osteopontin (OPN). The sensor has a low limit of detection (LOD), high sensitivity, and outstanding selectivity in complex biological media. We used this OPN immunosensor to continuously monitor on-chip osteogenesis of human mesenchymal stem cells (hMSCs) cultured 2D and 3D hydrogel constructs inside a microfluidic bioreactor for more than a month and were able to observe changing levels of OPN secretion during culture. The proposed platform can potentially be adopted for monitoring a variety of biological applications and further developed into a fully automated system for applications in advanced cellular biomanufacturing.

Nano-Brush Structure for Rapid Label-Free Differentiation of Alzheimer's Disease Stages and Direct Capture of Neuron-Derived Exosomes from Human Blood Plasma

The measurement of the neurofilament light chain (NFL) in human blood plasma/serum is a promising liquid biopsy for Alzheimer's disease (AD) diagnosis, offering advantages over conventional neuroimaging techniques recommended in clinical guidelines. Here, a controllable nano-brush structure comprising upstanding silicon nanowires coated with indium tin oxide was employed as the sensing substrate. This nano-brush structure was modified with an NFL antibody (NFLAb) via silane coupling and then further connected as the extended gate in a field-effect transistor (EGFET). Notable signal differences emerged within a 2 min timeframe, enabling the label-free differentiation in human blood plasmas among four distinct cohorts: healthy controls, subjective cognitive decline, mild cognitive impairment, and dementia due to AD. Our study indicates that achieving a surface roughness exceeding 400 nm on the modified nano-brush structure enables the effective electrical sensing in our EGFETs. These distinct electrical responses measured via the NFLAb-modified nano-brush EGFETs can be attributed to the combined effects of the captured NFLs and NFL-specific neuron-derived exosomes (NDEs) found in dementia patients, as confirmed by electron spectroscopy for chemical analysis, atomic force microscopy, and scanning electron microscopy. Finally, the potential of quantitatively detecting NDEs on the NFLAb-modified nano-brush structure was demonstrated using spiked solutions containing NFL-specific NDEs from IMR-32 neuroblast cells, wherein concentration-dependent changes were observed in the EGFETs output signal. Our findings show that the NFLAb-modified nano-brush EGFET enables rapid, label-free differentiation between healthy individuals and patients at varying stages of AD.

Designable microfluidic ladder networks from backstepping microflow analysis for mass production of monodisperse microdroplets

Controllable mass production of monodisperse droplets plays a key role in numerous fields ranging from scientific research to industrial application. Microfluidic ladder networks show great potential in mass production of monodisperse droplets, but their design with uniform microflow distribution remains challenging due to the lack of a rational design strategy. Here an effective design strategy based on backstepping microflow analysis (BMA) is proposed for the rational development of microfluidic ladder networks for mass production of controllable monodisperse microdroplets. The performance of our BMA rule for rational microfluidic ladder network design is demonstrated by using an existing analogism-derived rule that is widely used for the design of microfluidic ladder networks as the control group. The microfluidic ladder network designed by the BMA rule shows a more uniform flow distribution in each branch microchannel than that designed by the existing rule, as confirmed by single-phase flow simulation. Meanwhile, the microfluidic ladder network designed by the BMA rule allows mass production of droplets with higher size monodispersity in a wider window of flow rates and mass production of polymeric microspheres from such highly monodisperse droplet templates. The proposed BMA rule provides new insights into the microflow distribution behaviors in microfluidic ladder networks based on backstepping microflow analysis and provides a rational guideline for the efficient development of microfluidic ladder networks with uniform flow distribution for mass production of highly monodisperse droplets. Moreover, the BMA method provides a general analysis strategy for microfluidic networks with parallel multiple microchannels for rational scale-up.

Portable immunosensor directly and rapidly detects Mycobacterium tuberculosis in sputum

Tuberculosis (TB) remains a public health problem that cannot be ignored. The portable and efficient detection of Mycobacterium tuberculosis (MTB) is important for the effective control of this disease. However, current detection techniques do not meet the requirements for MTB detection in the actual environment and often require cumbersome detection steps that are time consuming and inflexible. In this study, a portable immunosensor to detect MTB in sputum was prepared and then subjected to interface characterizations, such as scanning electron microscopy, hydrophilic angle test, and fluorescence characterization. The source and gate voltage of the device were optimized and tested using a non-contact photoresponse. The results showed that the sensitivity of the sensor to luminance increases with the decrease in source voltage. The gate voltage can substantially improve the response of the immunosensor to the normalized current of protein and amplify the signal at least 1.6 times. The optimal voltage detection conditions of source voltage (0.3 V) and gate voltage (0.1 V) were also determined. Several common proteins present in simulated saliva were used for anti-interference tests, and the sensor exhibited good specificity. Finally, the dilution gradient of an actual TB sputum sample was optimized. In the absence of preconditioning, a double-blind experiment was used to distinguish between the sputum from patients with TB and healthy individuals to shorten the TB detection time to a few minutes. Compared with the hospital's conventional detection method using cultures, the proposed method can complete the detection in a shorter time. This study provides a new strategy for the portable diagnosis of TB.

Longitudinal Zeolite-Iron Oxide Nanocomposite Deposited Capacitance Biosensor for Interleukin-3 in Sepsis Detection

Sepsis is an extreme condition involving a physical response to severe microbial infection and causes fatal and life-threatening issues. Sepsis generates during the chemicals release with the immune system into the bloodstream for fighting against an infection, which causes the inflammation and leads to the medical emergency. A complexed longitudinal zeolite and iron oxide nanocomposite was extracted from coal mine fly ash and utilized to improve the surface characteristics of the capacitance biosensor to identify sepsis attacks. Anti-interleukin-3 (anti-IL-3) antibody was attached to the zeolite- and iron oxide-complexed capacitance electrode surface through an amine linker to interact with the sepsis biomarker IL-3. The morphological and chemical components of the nanocomplex were investigated by FESEM, FETEM, and EDX analyses. At approximately 30 nm, the longitudinal zeolite and iron oxide nanocomposite aided in attaining the limit of IL-3 detection of 3 pg/mL on the linear curve, with a regression coefficient (R2) of 0.9673 [y = 1.638x - 1.1847]. A lower detection limit was achieved in the dose-dependent range (3-100 pg/mL) due to the higher amount of antibody immobilization on the sensing surface due to the nanomaterials and the improved surface current. Furthermore, control experiments with relevant biomolecules did not show capacitance changes, and spiked IL-3 in human serum increased capacitance, indicating the specific and selective detection of IL-3. This study identifies and quantifies IL-3 via potentially useful methods and helps in diagnosing sepsis attack.

Sensitive silica-alumina modified capacitive non-Faradaic glucose sensor for gestational diabetes

A highly sensitive silica-alumina (Si-Al)-modified capacitive non-Faradaic glucose biosensor was introduced to monitor gestational diabetes. Glucose oxidase (GOx) was attached to the Si-Al electrode surface as the probe through amine-modification followed by glutaraldehyde premixed GOx as aldehyde-amine chemistry. This Si-Al (∼50 nm) modified electrode surface has increased the current flow upon binding of GOx with glucose. Capacitance values were increased by increasing the glucose concentrations. A mean capacitance value was plotted and the detection limit was found as 0.03 mg/mL with the regression coefficient value, R² = 0.9782 [y = 0.8391x + 1.338] on the linear range between 0.03 and 1 mg/mL. Further, a biofouling experiment with fructose and galactose did not increase the capacitance, indicating the specific glucose detection. This Si-Al-modified capacitance sensor detects a lower level of glucose presence and helps in monitoring gestational diabetes.

Hybrid Silicon Nanowire Devices and Their Functional Diversity

In the pool of nanostructured materials, silicon nanostructures are known as conventionally used building blocks of commercially available electronic devices. Their application areas span from miniaturized elements of devices and circuits to ultrasensitive biosensors for diagnostics. In this Review, the current trends in the developments of silicon nanowire-based devices are summarized, and their functionalities, novel architectures, and applications are discussed from the point of view of analog electronics, arisen from the ability of (bio)chemical gating of the carrier channel. Hybrid nanowire-based devices are introduced and described as systems decorated by, e.g., organic complexes (biomolecules, polymers, and organic films), aimed to substantially extend their functionality, compared to traditional systems. Their functional diversity is explored considering their architecture as well as areas of their applications, outlining several groups of devices that benefit from the coatings. The first group is the biosensors that are able to represent label-free assays thanks to the attached biological receptors. The second group is represented by devices for optoelectronics that acquire higher optical sensitivity or efficiency due to the specific photosensitive decoration of the nanowires. Finally, the so-called new bioinspired neuromorphic devices are shown, which are aimed to mimic the functions of the biological cells, e.g., neurons and synapses.

Capacitive aptasensor based on interdigitated electrode for breast cancer detection in undiluted human serum

We report the development of a simple and powerful capacitive aptasensor for the detection and estimation of human epidermal growth factor receptor 2 (HER2), a biomarker for breast cancer, in undiluted serum. The study involves the incorporation of interdigitated gold electrodes, which were used to prepare the electrochemical platform. A thiol terminated DNA aptamer with affinity for HER2 was used to prepare the bio-recognition layer via self-assembly on interdigitated gold surfaces. Non-specific binding was prevented by blocking free spaces on surface via starting block phosphate buffer saline-tween20 blocker. The sensor was characterized using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), atomic force microscopy and contact angle studies. Non-Faradic EIS measurements were utilized to investigate the sensor performance via monitoring of the changes in capacitance. The aptasensor exhibited logarithmically detection of HER2 from 1pM to 100nM in both buffer and undiluted serum with limits of detection lower than 1pM. The results pave the way to develop other aptamer-based biosensors for protein biomarkers detection in undiluted serum.

General Signal Amplification Strategy for Nonfaradic Impedimetric Sensing: Trastuzumab Detection Employing a Peptide Immunosensor

A label-free and reagent-free peptide mimotope capacitive biosensor has been developed for cancer drug (trastuzumab) quantification based on nonfaradic readout. The low sensitivity issue of capacitive biosensors was overcome with two innovations: peptide mimotope mixed self-assembled monolayer (SAM) biointerface and dilution of the analysis buffer. Signal amplification was achieved through dilution of phosphate-buffered saline (PBS) to tune C_dl to dominate the overall capacitance change upon target binding, which contribution is often negligible without dilution. After 1000× dilution, the limit of detection was lowered 500-fold (0.22 μg/mL) and the sensitivity was increased 20-fold [0.04192 (μg/mL)^-1] in comparison with undiluted PBS. The proposed signal amplification strategy is more straightforward and practical compared to biorecognition element engineering and other strategies. The proposed method was further applied to planar electrodes for optimizing sensing response time to less than 1 min.

Nano-Biosensor for Monitoring the Neural Differentiation of Stem Cells

In tissue engineering and regenerative medicine, monitoring the status of stem cell differentiation is crucial to verify therapeutic efficacy and optimize treatment procedures. However, traditional methods, such as cell staining and sorting, are labor-intensive and may damage the cells. Therefore, the development of noninvasive methods to monitor the differentiation status in situ is highly desirable and can be of great benefit to stem cell-based therapies. Toward this end, nanotechnology has been applied to develop highly-sensitive biosensors to noninvasively monitor the neural differentiation of stem cells. Herein, this article reviews the development of noninvasive nano-biosensor systems to monitor the neural differentiation of stem cells, mainly focusing on optical (plasmonic) and eletrochemical methods. The findings in this review suggest that novel nano-biosensors capable of monitoring stem cell differentiation are a promising type of technology that can accelerate the development of stem cell therapies, including regenerative medicine.

Highly Disordered Array of Silicon Nanowires: an Effective and Scalable Approach for Performing and Flexible Electrochemical Biosensors

The direct integration of disordered arranged and randomly oriented silicon nanowires (SiNWs) into ultraflexible and transferable electronic circuits for electrochemical biosensing applications is proposed. The working electrode (WE) of a three-electrode impedance device, fabricated on a polyimide (PI) film, is modified with SiNWs covered by a thin Au layer and functionalized to bind the sensing element. The biosensing behavior is investigated through the ligand-receptor binding of biotin-avidin system. Impedance measurements show a very efficient detection of the avidin over a broad range of concentrations from hundreds of micromolar down to the picomolar values. The impedance response is modeled through a simple equivalent circuit, which takes into account the unique WE morphology and its modification with successive layers of biomolecules. This approach of exploiting highly disordered SiNW ensemble in biosensing proves to be very promising for the following three main reasons: first, the system morphology allows high sensing performance; second, these nanostructures can be built via scalable and transferable fabrication methodology allowing an easy integration on non-conventional substrates; third, reliable modeling of the sensing response can be developed by considering the morphological and surface characteristics over an ensemble of disordered NWs rather than over individual NWs.