Development of microcantilever sensors for cell studies

Micro- and nano- electromechanical devices such as microcantilevers have paved the way for a large variety of new possibilities, such as the rapid diagnosis of diseases and a high throughput platform for drug discovery. Conventional cell assay methods rely on the addition of reagents, disrupting the measurement, therefore providing only the endpoint data of the cell growth experiment. In addition, these methods are typically slow to provide results and time and cost consuming. Therefore, microcantilever sensors are a great platform to conduct cell culturing experiments for cell culture, viability, proliferation, and cytotoxicity monitoring, providing advantages such as being able to monitor cell kinetics in real time without requiring external reagents, in addition to being low cost and fast, which conventional cell assay methods are unable to provide. This work aims to develop and test different types of microcantilever biosensors for the detection and monitoring of cell proliferation. This approach will overcome many of the current challenges facing microcantilever biosensors, including but not limited to achieving characteristics such as being low cost, rapid, easy to use, highly sensitive, label-free, multiplexed arrays, etc. Microcantilever sensor platforms utilizing both a single and scanning optical beam detection methods were developed and incorporated aspects such as temperature control, calibration, and readout schemes. Arrays of up to 16 or 32 microcantilever sensors can be simultaneously measured with integrated microfluidic channels. The effectiveness of these cantilever platforms are demonstrated through multiple studies, including examples of growth induced bending of polyimide cantilevers for simple real-time yeast cell measurements and a microcantilever array for rapid, sensitive, and real-time measurement of nanomaterial toxicity on the C3A human liver cell line. In addition, other techniques for microcantilever arrays and microfluidics will be presented along with demonstrations for the ability for stem cell growth monitoring and pathogen detection

Nucleic Acid-based Detection of Bacterial Pathogens Using Integrated Microfluidic Platform Systems

The advent of nucleic acid-based pathogen detection methods offers increased sensitivity and specificity over traditional microbiological techniques, driving the development of portable, integrated biosensors. The miniaturization and automation of integrated detection systems presents a significant advantage for rapid, portable field-based testing. In this review, we highlight current developments and directions in nucleic acid-based micro total analysis systems for the detection of bacterial pathogens. Recent progress in the miniaturization of microfluidic processing steps for cell capture, DNA extraction and purification, polymerase chain reaction, and product detection are detailed. Discussions include strategies and challenges for implementation of an integrated portable platform

Micro and nano technology platforms: From cell viability monitoring to FET based biosensing

Nanotechnology is a multidisciplinary field that combines science and engineering to design, synthesize, characterize and explore applications for materials and devices whose smallest functional organization in at least one dimension is on the nanometer scale. Nanotechnology is undergoing an explosive development and the extent of potential application is vast and widely diverse. In the field of human health care, nanotechnology is helping to develop novel materials and structures, which have made it possible to miniaturize many of the tools used in conventional assays. Smart biochips constructed out of these novel materials and structures are now capable of performing limited in vitro diagnostic tests involved in immunoassays. In this work, we report two devices that make use of micro scale and/or nano scale structures to contribute to the ever-expanding use of biochips in human health care. The first device is a Patch-Clamp microchip that is capable of monitoring cell viability in real-time. It is critical to monitor the health of cells in biological life science and medical research. Researchers must know if a new drug is capable of killing cancer cells or in other cases to determine the toxic effects of a drug or a pesticide on healthy cells. Conventional cell viability monitoring techniques that use flow cytometer or fluorescent dyes in conjunction with fluorescence microscope are time consuming and require sample labeling. Alternatively, we have designed a patch-clamp microchip, which allows one to measure the ion-channel currents in real-time. This microchip provides a faster and label-free platform to monitor the health of the cell. Simultaneously, viability tests were performed on four different types of cancer cells (MB231, MB231-BR-vector, MB231-BR-HER 2, and MB231-BR) using the conventional fluorescent dye technique and using the patch-clamp microchip technique. For the patch-clamp technique, the seal resistance of the device decreased from ∼22 MΩ, (living cell) to ∼4 MΩ (dead cell) over a period of 120 minutes. Comparing the seal resistance to the intensity of the fluorescence images over the 120 minute period confirms a correlation between the health of the cell and the ion-channel current, validating our claim that the patch-clamp microchip can be used as an alternate technical platform to the conventional techniques that use fluorescent dyes or a flow cytometer. The second device is a Field-Effect Transistor (FET) based biosensor used for the detection of biomolecules. The conventional technique, ELISA, is still the gold standard for immunoassays. Most of the modern biosensors have exploited the semi conductive nature of CNT to design a label-free FET based immunosensor (biosensor that exclusively monitors the antibody-antigen interaction). Even though biosensors made out of a single CNT are ideally capable of detecting a single molecule, the fabrication of such devices is challenging. To avoid the fabrication complexity involved with a single CNT based immunosensor, we have developed an FET based biosensor, in which the channel is made out of Carbon Nanotube Thin Film (CNTF). The CNTF channel between the source and drain electrodes is assembled using electrostatic layer-by-layer (LBL) self-assembly. The bio-affinity interaction between Protein A and rabbit IgG is used to model the antibody-antigen interaction, and our initial results show the device is capable of detecting IgG concentrations as low as 1 pg/mL

Optoelectronic Capillary Sensors in Microfluidic and Point-of-Care Instrumentation

This paper presents a review, based on the published literature and on the authors’ own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors

Sensitive and specific detection of E. coli using biomimetic receptors in combination with a modified heat-transfer method

We report on a novel biomimetic sensor that allows sensitive and specific detection of Escherichia colt (E. coli) bacteria in a broad concentration range from 10(2) up to 10(6) CFU/mL in both buffer fluids and relevant food samples (i.e. apple juice). The receptors are surface-imprinted polyurethane layers deposited on stainless-steel chips. Regarding the transducer principle, the sensor measures the increase in thermal resistance between the chip and the liquid due to the presence of bacteria captured on the receptor surface. The low noise level that enables the low detection limit originates from a planar meander element that serves as both a heater and a temperature sensor. Furthermore, the experiments show that the presence of bacteria in a liquid enhances the thermal conductivity of the liquid itself. Reference tests with a set of other representative species of Enterobacteriaceae, closely related to E. coli, indicate a very low cross-sensitivity with a sensor response at or below the noise level

Structure and Applications of Gold in Nanoporous Form

Nanoporous gold (np-Au) has many interesting and useful properties that make it a material of interest for use in many technological applications. Its biocompatible nature and ability to serve as a support for self-assembled monolayers of alkanethiols and their derivative make it a suitable support for the immobilization of carbohydrates, enzymes, proteins, and DNA. Its chemically inert, physically robust and conductive high-surface area makes it useful for the design of electrochemistry-based chemical/bio-sensors and reactors. Furthermore, it is also used as solid support for organic molecular synthesis and biomolecules separation. Its enhanced optical property has application in design of plasmonics-based sensitive biosensors. In fact, np-Au is one of the few materials that can be used as a transducer for both optical and electrochemical biosensing. Due to the presence of low-coordination surface sites, np-Au shows remarkable catalytic activity for oxidation of molecules like carbon monoxide and methanol. Owing to the importance of np-Au, in this chapter we will highlight different strategies of fabrication of np-Au and its emerging applications based on its unique properties

Optical biosensors - Illuminating the path to personalized drug dosing

Optical biosensors are low-cost, sensitive and portable devices that are poised to revolutionize the medical industry. Healthcare monitoring has already been transformed by such devices, with notable recent applications including heart rate monitoring in smartwatches and COVID-19 lateral flow diagnostic test kits. The commercial success and impact of existing optical sensors has galvanized research in expanding its application in numerous disciplines. Drug detection and monitoring seeks to benefit from the fast-approaching wave of optical biosensors, with diverse applications ranging from illicit drug testing, clinical trials, monitoring in advanced drug delivery systems and personalized drug dosing. The latter has the potential to significantly improve patients' lives by minimizing toxicity and maximizing efficacy. To achieve this, the patient's serum drug levels must be frequently measured. Yet, the current method of obtaining such information, namely therapeutic drug monitoring (TDM), is not routinely practiced as it is invasive, expensive, time-consuming and skilled labor-intensive. Certainly, optical sensors possess the capabilities to challenge this convention. This review explores the current state of optical biosensors in personalized dosing with special emphasis on TDM, and provides an appraisal on recent strategies. The strengths and challenges of optical biosensors are critically evaluated, before concluding with perspectives on the future direction of these sensors

Microfluidic devices for photo-and spectroelectrochemical applications

The review presents recent developments in electrochemical devices for photo- and spectroelectrochemical investigations, with the emphasis on miniaturization (i.e., nanointerdigitated complementary metal-oxide-semiconductor devices, micro- and nano-porous silicon membranes or microoptoelectromechanical systems), silica glass/microreactors (i.e., plasmonic, Raman spectroscopy or optical microcavities) or polymer-based devices (i.e., 3D-printed, laser-engraved channels). Furthermore, we have evaluated inter alia the efficiency of various fabrication approaches for bioelectrochemical systems, biocatalysis, photochemical synthesis, or single nanoparticle spectroelectrochemistry. We envisioned the miniaturization of applied techniques such as cathodoluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy, voltametric and amperometric methods in the spectroelectrochemical microdevices. The research challenges and development perspectives of microfluidic, and spectroelectrochemical devices were also elaborated on.publishedVersio

Nanostructured metallic surfaces of Au implemented as electrochemical glucose sensors

Diabetes is one of the most prevalent chronic diseases growing globally with 450 million people currently being diagnosed with the disease. With this number dramatically increasing every year the need for highly sensitive and selective glucose sensors are of great importance. Along with this, the comfort of the patient when analysing their glucose concentrations has come to the forefront of research with the push towards non-invasive sensing devices becoming the major focus in this research. The aim of this research was to develop Au-based nanostructures and study their effectiveness in detecting ultra-low concentrations (<100 µM) of glucose. Au has shown excellent biocompatibility as well as its ability to be moulded for shape, size and density which can be tailored specifically to get enhanced glucose electrooxidation. Following a thorough literature review, the materials that were developed and investigated were pure mono-metallic Au structures, Au Pt alloy and Au Ni particles as well as Au Co3O4 composites. Initially, a pure nanostructure of Au was studied in the form of Au nanospikes where the impact of HAuCl4 concentration, Pb acetate concentration (growth agent for shape), electrodeposition time and electrodeposition potential were studied. From these studies the optimal conditions to produce Au nanospikes for optimal glucose sensing were found to have a HAuCl4 concentration of 13.6 mM, a Pb acetate concentration of 1 mM, an electrodeposition time of 12 mins and an applied electrodeposition potential of +0.05 V. Analysis of this optimal pure Au sensor was performed with calculated sensitivity of 91.8 µA·mM-1·cm-2 with no interference from common physiological contaminants making this sensor sensitive and highly selective. Further study of the Au-based sensors pushed the study to use Au in conjunction with Pt in an alloyed form. Using the hydrogen bubble template technique with varying concentrations of Pt were used to form a sensor with a very large electrochemical surface area (ECSA). In this study various concentrations of Pt were added to the electrodeposition solution with 0.5 mM of Pt showing the largest overall surface area and the highest sensitivity in the presence of glucose. Electrochemical glucose sensing analysis was performed on the Au-Pt alloyed sensor producing a high sensitivity of 109.3 µA·mM-1·cm-2 showing the alloyed material produced a higher sensitivity than that of the monometallic Au sensor. With the addition of Pt, a higher sensitivity was obtained whist the large presence of Au allowed for the sensor to have excellent selectivity in the presence of common physiological contaminants which has previously hindered the use of Pt in glucose sensing nanostructures. To reduce Au content yet increase sensitivity, highly active Au nanoparticles on a Ni platform were employed. It is well known that Au nanoparticles grown by galvanic replacement are highly active however a uniform formation is a major challenge due to the mechanism by which a galvanic replacement reaction occurs. From this knowledge, Ni colloidal crystals were employed to attempt to overcome this issue. Multiple concentrations of Au were used to determine the optimal concentration of Au which was found to be 0.1 mM of HAuCl4. Analysis of this formed sensor was performed and a very large sensitivity of 506 µA·mM-1·cm-2 showing a much larger enhancement of sensitivity compared to both the pure Au and Au-Pt alloyed sensors. The Ni-Au colloidal sensor showed minimal effect from common physiological contaminants due to the presence of Au in the structure. Finally, a study of the effect of an additional material was studied in the presence of the metal oxide Co3O4 due to its excellent biocompatibility and excellent sensitivity in the presence of glucose. The hydrogen bubble templated technique was used to form a pure Au lattice structure which was then coated in pure Co3O4 nanowires using the hydrothermal technique. The formed structure had a completely cohesive structure where Co3O4 moulded over the Au allowing for synchronized sensing between the Au and Co3O4 components to occur. The electrochemical sensing analysis of the Au-Co3O4 structure showed a huge sensitivity of 2014 µA·mM-1·cm-2 within the glucose concentration range between 0.02 and 1 mM. This large sensitivity in the low region of glucose concentrations showed the possibility of the sensor performing successfully within the glucose concentration range of saliva (20 ¿ 1000 µM). Further analysis of the sensor was performed in the presence of synthetic saliva showing an excellent linearity of glucose additions and minimal to no effect from common physiological contaminants found in saliva. These findings showed the feasibility of the developed electrochemical glucose sensor to be employed for non-invasive diabetes monitoring and diagnostic applications