Bioinks and biofabrication techniques for biosensors development: A review

3D bioprinting technologies and bioink development are enabling significant advances in miniaturized and integrated biosensors. For example, bioreceptors can be immobilized within a porous 3D structure to significantly amplify the signal, while biocompatible and mechanically flexible systems uniquely enable wearable chem- and bio-sensors. This advancement is accelerating translation by enabling the production of high performance, reproducible, and flexible analytical devices. The formulation of the bioink plays a crucial role in determining the bio-functionality of the resulting printed structures, e.g., the porosity that allows the analyte to diffuse through the 3D structure, the affinity and avidity of the receptors, etc. This review explores the next generation of advanced bioinks for biosensor development and provides insights into the latest cutting-edge bioprinting technologies. The bioprinting methods available for biosensor fabrication including inkjet, extrusion, and laser-based bioprinting, are discussed. The advantages and limitations of each method are analysed, and recent advancements in bioprinting technologies are presented. The review then delves into the properties of advanced bioinks, such as biocompatibility, printability, stability, and applicability. Different types of advanced bioinks are explored, including multicomponent, stimuli-responsive, and conductive bioinks. Finally, the next generation of bioinks for biosensors is considered, identifying possible new opportunities and challenges. Overall, this literature review highlights the combined importance of bioink formulation and bioprinting methods for the development of high-performance analytical biosensors.

Fully printed and self-compensated bioresorbable electrochemical devices based on galvanic coupling for continuous glucose monitoring

Real-time glucose monitoring conventionally involves non-bioresorbable semi-implantable glucose sensors, causing infection and pain during removal. Despite bioresorbable electronics serves as excellent alternatives, the bioresorbable sensor dissolves in aqueous environments with interferential biomolecules. Here, the theories to achieve stable electrode potential and accurate electrochemical detection using bioresorbable materials have been proposed, resulting in a fully printed bioresorbable electrochemical device. The adverse effect caused by material degradation has been overcome by a molybdenum-tungsten reference electrode that offers stable potential through galvanic-coupling and self-compensation modules. In vitro and in vivo glucose monitoring has been conducted for 7 and 5 days, respectively, followed by full degradation within 2 months. The device offers a glucose detection range of 0 to 25 millimolars and a sensitivity of 0.2458 microamperes per millimolar with anti-interference capability and biocompatibility, indicating the possibility of mass manufacturing high-performance bioresorbable electrochemical devices using printing and low-temperature water-sintering techniques. The mechanisms may be implemented developing more comprehensive bioresorbable sensors for chronic diseases.

A Nanotechnology-Based Approach to Biosensor Application in Current Diabetes Management Practices

Diabetes mellitus is linked to both short-term and long-term health problems. Therefore, its detection at a very basic stage is of utmost importance. Research institutes and medical organizations are increasingly using cost-effective biosensors to monitor human biological processes and provide precise health diagnoses. Biosensors aid in accurate diabetes diagnosis and monitoring for efficient treatment and management. Recent attention to nanotechnology in the fast-evolving area of biosensing has facilitated the advancement of new sensors and sensing processes and improved the performance and sensitivity of current biosensors. Nanotechnology biosensors detect disease and track therapy response. Clinically efficient biosensors are user-friendly, efficient, cheap, and scalable in nanomaterial-based production processes and thus can transform diabetes outcomes. This article is more focused on biosensors and their substantial medical applications. The highlights of the article consist of the different types of biosensing units, the role of biosensors in diabetes, the evolution of glucose sensors, and printed biosensors and biosensing systems. Later on, we were engrossed in the glucose sensors based on biofluids, employing minimally invasive, invasive, and noninvasive technologies to find out the impact of nanotechnology on the biosensors to produce a novel device as a nano-biosensor. In this approach, this article documents major advances in nanotechnology-based biosensors for medical applications, as well as the hurdles they must overcome in clinical practice.

Challenges, Prospects, and Emerging Applications of Inkjet-Printed Electronics: A Chemist's Point of View

Driven by the development of new functional inks, inkjet-printed electronics has achieved several milestones upon moving from the integration of simple electronic elements (e.g., temperature and pressure sensors, RFID antennas, etc.) to high-tech applications (e.g. in optoelectronics, energy storage and harvesting, medical diagnosis). Currently, inkjet printing techniques are limited by spatial resolution higher than several micrometers, which sets a redhibitorythreshold for miniaturization and for many applications that require the controlled organization of constituents at the nanometer scale. In this Review, we present the physico-chemical concepts and the equipment constraints underpinning the resolution limit of inkjet printing and describe the contributions from molecular, supramolecular, and nanomaterials-based approaches for their circumvention. Based on these considerations, we propose future trajectories for improving inkjet-printing resolution that will be driven and supported by breakthroughs coming from chemistry. Please check all text carefully as extensive language polishing was necessary. Title ok? Yes.

Inkjet Printing: A Viable Technology for Biosensor Fabrication

Printing technology promises a viable solution for the low-cost, rapid, flexible, and mass fabrication of biosensors. Among the vast number of printing techniques, screen printing and inkjet printing have been widely adopted for the fabrication of biosensors. Screen printing provides ease of operation and rapid processing; however, it is bound by the effects of viscous inks, high material waste, and the requirement for masks, to name a few. Inkjet printing, on the other hand, is well suited for mass fabrication that takes advantage of computer-aided design software for pattern modifications. Furthermore, being drop-on-demand, it prevents precious material waste and offers high-resolution patterning. To exploit the features of inkjet printing technology, scientists have been keen to use it for the development of biosensors since 1988. A vast number of fully and partially inkjet-printed biosensors have been developed ever since. This study presents a short introduction on the printing technology used for biosensor fabrication in general, and a brief review of the recent reports related to virus, enzymatic, and non-enzymatic biosensor fabrication, via inkjet printing technology in particular.

Study of the Enzyme Activity Change due to Inkjet Printing for Biosensor Fabrication

Enzymes, the most commonly used biosensing element, have a great influence on the performance of biosensors. Recently, drop-on-demand (DOD) printing technique has been widely employed for the fabrication of biosensors due to its merits of noncontact, less waste, and rapid deposition. However, enzyme printing studies were rarely conducted on the effect of printing parameters from the aspect of the pressure wave propagation mechanism. This study investigated the effects of pressure wave propagation on enzyme activity from the aspects of wave superposition, wave amplitude, resulting mechanical stress, and protein conformation change using pyruvate oxidase as the model enzyme. We found that the mechanical stress increased the activity of pyruvate oxidase during the inkjet printing process. A shear rate of 3 × 10⁵ s^-1 enhanced the activity by 14.10%. The enhancement mechanism was investigated, and the mechanical activation or mild proteolysis was found to change the conformation of pyruvate oxidase and improve its activity. This study is fundamental to understand the effect of both printing mechanism and induced mechanical stress on the properties of biomolecules and plays an important role in modulating the activity of other enzyme-based inks, which is crucial for the development of biosensors.

All-Inkjet-Printed Flexible Nanobio-Devices with Efficient Electrochemical Coupling Using Amphiphilic Biomaterials

Nanostructured flexible electrodes with biological compatibility and intimate electrochemical coupling provide attractive solutions for various emerging bioelectronics and biosensor applications. Here, we develop all-inkjet-printed flexible nanobio-devices with excellent electrochemical coupling by employing amphiphilic biomaterial, an M13 phage, numerical simulation of single-drop formulation, and rational formulations of nanobio-ink. Inkjet-printed nanonetwork-structured electrodes of single-walled carbon nanotubes and M13 phage show efficient electrochemical coupling and hydrostability. Additive printing of the nanobio-inks also allows for systematic control of the physical and chemical properties of patterned electrodes and devices. All-inkjet-printed electrochemical field-effect transistors successfully exhibit pH-sensitive electrical current modulation. Moreover, all-inkjet-printed electrochemical biosensors fabricated via sequential inkjet-printing of the nanobio-ink, electrolytes, and enzyme solutions enable direct electrical coupling within the printed electrodes and detect glucose concentrations at as low as 20 μM. Glucose levels in sweat are successfully measured, and the change in sweat glucose levels is shown to be highly correlated with blood glucose levels. Synergistic combination of additive fabrication by inkjet-printing with directed assembly of nanostructured electrodes by functional biomaterials could provide an efficient means of developing bioelectronic devices for personalized medicine, digital healthcare, and emerging biomimetic devices.

Recent advances in micro- and nano-bubbles for atherosclerosis applications

Micro- and nano-bubbles have been developed as powerful multimodal theranostic agents for atherosclerosis treatment.

Conjugated Polymers for Assessing and Controlling Biological Functions

The field of organic bioelectronics is advancing rapidly in the development of materials and devices to precisely monitor and control biological signals. Electronics and biology can interact on multiple levels: organs, complex tissues, cells, cell membranes, proteins, and even small molecules. Compared to traditional electronic materials such as metals and inorganic semiconductors, conjugated polymers (CPs) have several key advantages for biological interactions: tunable physiochemical properties, adjustable form factors, and mixed conductivity (ionic and electronic). Herein, the use of CPs in five biologically oriented research topics, electrophysiology, tissue engineering, drug release, biosensing, and molecular bioelectronics, is discussed. In electrophysiology, implantable devices with CP coating or CP-only electrodes are showing improvements in signal performance and tissue interfaces. CP-based scaffolds supply highly favorable static or even dynamic interfaces for tissue engineering. CPs also enable delivery of drugs through a variety of mechanisms and form factors. For biosensing, CPs offer new possibilities to incorporate biological sensing elements in a conducting matrix. Molecular bioelectronics is today used to incorporate (opto)electronic functions in living tissue. Under each topic, the limits of the utility of CPs are discussed and, overall, the major challenges toward implementation of CPs and their devices to real-world applications are highlighted.

Inkjet Printing for Biomedical Applications

Inkjet printing can deposit politer volumes of a specified ink at precise locations on a substrate. Here we describe methods of using inkjet printing for cell patterning in the field of biomedical applications, either directly printing cells in cell media, or indirectly through printing a wax scaffold that guides cell orientation/attachment onto a substrate.

Functional nanostructures for enzyme based biosensors: properties, fabrication and applications

A review describing functional nanostructures for portable and printable enzyme biosensors. Specific physicochemical and surface properties of nanoparticles used as carriers and sensing components and their assembly are discussed with an overview of current and emerging techniques enabling large scale roll-to-roll fabrication and miniaturization. Their integration in flexible, wearable and inexpensive point-of-use devices, and implementation challenges are also provided with examples of applications.

Inkjet printing for biosensor fabrication: combining chemistry and technology for advanced manufacturing

Inkjet printing is emerging at the forefront of biosensor fabrication technologies. Parallel advances in both ink chemistry and printers have led to a biosensor manufacturing approach that is simple, rapid, flexible, high resolution, low cost, efficient for mass production, and extends the capabilities of devices beyond other manufacturing technologies. Here we review for the first time the factors behind successful inkjet biosensor fabrication, including printers, inks, patterning methods, and matrix types. We discuss technical considerations that are important when moving beyond theoretical knowledge to practical implementation. We also highlight significant advances in biosensor functionality that have been realised through inkjet printing. Finally, we consider future possibilities for biosensors enabled by this novel combination of chemistry and technology.

A Low-Cost Inkjet-Printed Glucose Test Strip System for Resource-Poor Settings

BACKGROUND

The prevalence of diabetes is increasing in low-resource settings; however, accessing glucose monitoring is extremely difficult and expensive in these regions. Work is being done to address the multitude of issues surrounding diabetes care in low-resource settings, but an affordable glucose monitoring solution has yet to be presented. An inkjet-printed test strip solution is being proposed as a solution to this problem.

METHODS

The use of a standard inkjet printer is being proposed as a manufacturing method for low-cost glucose monitoring test strips. The printer cartridges are filled with enzyme and dye solutions that are printed onto filter paper. The result is a colorimetric strip that turns a blue/green color in the presence of blood glucose.

RESULTS

Using a light-based spectroscopic reading, the strips show a linear color change with an R(2) = .99 using glucose standards and an R(2) = .93 with bovine blood. Initial testing with bovine blood indicates that the strip accuracy is comparable to the International Organization for Standardization (ISO) standard 15197 for glucose testing in the 0-350 mg/dL range. However, further testing with human blood will be required to confirm this. A visible color gradient was observed with both the glucose standard and bovine blood experiment, which could be used as a visual indicator in cases where an electronic glucose meter was unavailable.

CONCLUSIONS

These results indicate that an inkjet-printed filter paper test strip is a feasible method for monitoring blood glucose levels. The use of inkjet printers would allow for local manufacturing to increase supply in remote regions. This system has the potential to address the dire need for glucose monitoring in low-resource settings.

Woven electrochemical fabric-based test sensors (WEFTS): a new class of multiplexed electrochemical sensors

We present textile weaving as a new technique for the manufacture of miniature electrochemical sensors with significant advantages over current fabrication techniques. Biocompatible silk yarn is used as the material for fabrication instead of plastics and ceramics used in commercial sensors. Silk yarns are coated with conducting inks and reagents before being handloom-woven as electrodes into patches of fabric to create arrays of sensors, which are then laminated, cut and packaged into individual sensors. Unlike the conventionally used screen-printing, which results in wastage of reagents, yarn coating uses only as much reagent and ink as required. Hydrophilic and hydrophobic yarns are used for patterning so that sample flow is restricted to a small area of the sensor. This simple fluidic control is achieved with readily available materials. We have fabricated and validated individual sensors for glucose and hemoglobin and a multiplexed sensor, which can detect both analytes. Chronoamperometry and differential pulse voltammetry (DPV) were used to detect glucose and hemoglobin, respectively. Industrial quantities of these sensors can be fabricated at distributed locations in the developing world using existing skills and manufacturing facilities. We believe such sensors could find applications in the emerging area of wearable sensors for chemical testing.

Printed and flexible biosensor for antioxidants using interdigitated ink-jetted electrodes and gravure-deposited active layer

Printing techniques have been extensively used in the fabrication of organic electronic devices, such as light-emitting diodes and display backplanes. These techniques, in particular inkjet printing, are being employed for the localized dispensing of solutions containing biological molecules and cells, leading to the fabrication of bio-functional microarrays and biosensors. Here, we report the fabrication of an all-printed and flexible biosensor for antioxidants. Gold (Au) interdigitated electrodes (IDEs) with sub-100 µm features were directly inkjet-printed on plastic substrates using a nanoparticle-based ink. Conductivities as high as 5×10(6) S/m (12% of bulk Au) were attained after sintering was conducted at plastic-compatible 200 °C for 6 h. The enzyme Tyrosinase (Tyr) was used in the active layer of the biosensors, being innovatively deposited by large-area rotogravure printing. A tailor-made ink was studied, and the residual activity of the enzyme was 85% after additives incorporation, and 15.5% after gravure printing. Au IDEs were coated with gravure films of the Tyr-containing ink, and the biosensor was encapsulated with a cellulose acetate dip-coating film to avoid dissolution. The biosensor impedance magnitude increases linearly with the concentration of a model antioxidant, allowing for the construction of a calibration curve. Control experiments demonstrated the molecular recognition characteristic inferred by the enzyme. We found that the biosensor sensitivity and the limit of detection were, respectively, 5.68 Ω/µm and 200 µM. In conclusion, a disposable, light-weight, all-printed and flexible biosensor for antioxidants was successfully fabricated using fast and large-area printing techniques. This opens the door for the fabrication of technological products using roll-to-roll processes.

Versatile, kinetically controlled, high precision electrohydrodynamic writing of micro/nanofibers

Direct writing of hierarchical micro/nanofibers have recently gained popularity in flexible/stretchable electronics due to its low cost, simple process and high throughput. A kinetically controlled mechanoelectrospinning (MES) is developed to directly write diversified hierarchical micro/nanofibers in a continuous and programmable manner. Unlike conventional near-field electrospinning, our MES method introduces a mechanical drawing force, to simultaneously enhance the positioning accuracy and morphology controllability. The MES is predominantly controlled by the substrate speed, the nozzle-to-substrate distance, and the applied voltage. As a demonstration, smooth straight, serpentine, self-similar, and bead-on-string structures are direct-written on silicon/elastomer substrates with a resolution of 200 nm. It is believed that MES can promote the low-cost, high precision fabrication of flexible/stretchable electronics or enable the direct writing of the sacrificial structures for nanoscale lithography.