Investigation of microfabrication of biological sample arrays using piezoelectric and bubble-jet printing technologies

Inkjet Printing of Pharmaceuticals

Inkjet printing (IJP) is an additive manufacturing process that selectively deposits ink materials, layer-by-layer, to create 3D objects or 2D patterns with precise control over their structure and composition. This technology has emerged as an attractive and versatile approach to address the ever-evolving demands of personalized medicine in the healthcare industry. Although originally developed for nonhealthcare applications, IJP harnesses the potential of pharma-inks, which are meticulously formulated inks containing drugs and pharmaceutical excipients. Delving into the formulation and components of pharma-inks, the key to precise and adaptable material deposition enabled by IJP is unraveled. The review extends its focus to substrate materials, including paper, films, foams, lenses, and 3D-printed materials, showcasing their diverse advantages, while exploring a wide spectrum of therapeutic applications. Additionally, the potential benefits of hardware and software improvements, along with artificial intelligence integration, are discussed to enhance IJP's precision and efficiency. Embracing these advancements, IJP holds immense potential to reshape traditional medicine manufacturing processes, ushering in an era of medical precision. However, further exploration and optimization are needed to fully utilize IJP's healthcare capabilities. As researchers push the boundaries of IJP, the vision of patient-specific treatment is on the horizon of becoming a tangible reality.

A novel array-type microdroplet parallel-generation device

In this study, the innovative design of a new array microdroplet parallel-generation device is proposed based on the principle of fluid inertial force using a capillary glass needle. The entire device used an electromagnetic actuator as the power source. It was designed as a 9-channel parallel array of glass needles. All glass needles feed independently, allowing different solutions to be sprayed simultaneously while effectively avoiding cross-contamination. We achieved non-contact parallel precision dispensing of nanoliter-sized microdroplet arrays using a relatively simple method. In this study, we first investigated the homogeneity of the generated droplet arrays and the stability of the device over long periods of operation. Then, the influence of the driving-voltage amplitude of the electromagnet and nozzle diameter on microdroplet generation was analyzed. Finally, a prediction model for the droplet size was developed using regression analysis to investigate the on-demand generation of droplets. In summary, the device designed in this study had a novel design, low cost, and modular assembly. It has excellent potential for applications in high precision and low-volume microdroplet-array generation.

A thermal ink-jet printing approach for evaluating susceptibility of bacteria to antibiotics

An inexpensive method for determining minimum inhibitory concentrations (MIC) using ink-jet printing to deposit drug solutions and bacterial suspensions onto agar was developed. Substrate concentrations were varied using a "Y-value", whereby a series of rectangles with the same width and colour but different heights were printed within a fixed unit area. Prior to MIC determination, the printer cartridges used were calibrated using Fast Green dye. The impact of thermal ink-jet printing on bacterial viability was assessed by colony counting and found not to be deleterious. MIC determinations were conducted by printing varying concentrations of the antibiotics onto agar-coated glass slides then printing a thin even film of a known bacterial density of Lactobacillus acidophilus. Broth microdilution was performed simultaneously to validate the results. Slides and well plates were then incubated anaerobically for 48 h. The MIC values obtained for the antibiotics used were within a permissible range for comparison.

Inkjet-Printed Paper Fluidic Devices for Onsite Detection of Antibiotics Using Surface-Enhanced Raman Spectroscopy

Surface enhanced Raman spectroscopy (SERS) provides rapid and sensitive identification of small molecule analytes. Traditionally, fabrication of SERS devices is an expensive process that involves the use of micro- and nano-fabrication procedures. Further, acquisition of diverse sample types requires complex preparation procedures that limits SERS to lab-based applications. Recent innovations using plasmonic nanoparticles embedded in flexible paper substrates has allowed the expansion of SERS techniques to portable analytical procedures. Recently inkjet-printing has been identified as a low cost, rapid, and highly customizable method for producing paper based SERS sensors with robust performance. This chapter details the materials and procedures by which inkjet printed SERS sensors can be fabricated and applied to relevant applications. In particular, methods for utilizing the sensors for detection of antibiotics are presented.

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.

Inkjet printing for pharmaceutics - A review of research and manufacturing

Global regulatory, manufacturing and consumer trends are driving a need for change in current pharmaceutical sector business models, with a specific focus on the inherently expensive research costs, high-risk capital-intensive scale-up and the traditional centralised batch manufacturing paradigm. New technologies, such as inkjet printing, are being explored to radically transform pharmaceutical production processing and the end-to-end supply chain. This review provides a brief summary of inkjet printing technologies and their current applications in manufacturing before examining the business context driving the exploration of inkjet printing in the pharmaceutical sector. We then examine the trends reported in the literature for pharmaceutical printing, followed by the scientific considerations and challenges facing the adoption of this technology. We demonstrate that research activities are highly diverse, targeting a broad range of pharmaceutical types and printing systems. To mitigate this complexity we show that by categorising findings in terms of targeted business models and Active Pharmaceutical Ingredient (API) chemistry we have a more coherent approach to comparing research findings and can drive efficient translation of a chosen drug to inkjet manufacturing.

Protein Microarrays with Novel Microfluidic Methods: Current Advances

Microfluidic-based micromosaic technology has allowed the pattering of recognition elements in restricted micrometer scale areas with high precision. This controlled patterning enabled the development of highly multiplexed arrays multiple analyte detection. This arraying technology was first introduced in the beginning of 2001 and holds tremendous potential to revolutionize microarray development and analyte detection. Later, several microfluidic methods were developed for microarray application. In this review we discuss these novel methods and approaches which leverage the property of microfluidic technologies to significantly improve various physical aspects of microarray technology, such as enhanced imprinting homogeneity, stability of the immobilized biomolecules, decreasing assay times, and reduction of the costs and of the bulky instrumentation.

Large-area molecular patterning with polymer pen lithography

The challenge of constructing surfaces with nanostructured chemical functionality is central to many areas of biology and biotechnology. This protocol describes the steps required for performing molecular printing using polymer pen lithography (PPL), a cantilever-free scanning probe-based technique that can generate sub-100-nm molecular features in a massively parallel fashion. To illustrate how such molecular printing can be used for a variety of biologically relevant applications, we detail the fabrication of the lithographic apparatus and the deposition of two materials, an alkanethiol and a polymer onto a gold and silicon surface, respectively, and show how the present approach can be used to generate nanostructures composed of proteins and metals. Finally, we describe how PPL enables researchers to easily create combinatorial arrays of nanostructures, a powerful approach for high-throughput screening. A typical protocol for fabricating PPL arrays and printing with the arrays takes 48-72 h to complete, including two overnight waiting steps.

Microfluidic parallel patterning and cellular delivery of molecules with a nanofountain probe

This brief report describes a novel tool for microfluidic patterning of biomolecules and delivery of molecules into cells. The microdevice is based on integration of nanofountain probe (NFP) chips with packaging that creates a closed system and enables operation in liquid. The packaged NFP can be easily coupled to a micro/nano manipulator or atomic force microscope for precise position and force control. We demonstrate here the functionality of the device for continuous direct-write parallel patterning on a surface in air and in liquid. Because of the small volume of the probes (~3 pL), we can achieve flow rates as low as 1 fL/s and have dispensed liquid drops with submicron to 10 µm diameters in a liquid environment. Furthermore, we demonstrate that this microdevice can be used for delivery of molecules into single cells by transient permeabilization of the cell membrane (i.e., electroporation). The significant advantage of NFP-based electroporation compared with bulk electroporation and other transfection techniques is that it allows for precise and targeted delivery while minimizing stress to the cell. We discuss the ongoing development of the tool toward automated operation and its potential as a multifunctional device for microarray applications and time-dependent single-cell studies.

Inkjet printing and release of monodisperse liquid crystal droplets from solid surfaces

Recently, liquid crystal (LC) droplets in aqueous solutions have become a new platform for chemical and biological sensing applications. In this work, we present a two-step method to generate monodisperse LC droplets in aqueous solutions for sensing applications. In the first step, we exploit inkjet printing to dispense uniform LC droplets on a solid surface. Uniform LC droplets, ranging from 35 to 136 μm in diameter, can be prepared by printing multiple times on the same spot. In the second step, we flush the LC droplets with a stream of aqueous solution in an open rectangular channel. Factors that determine the polydispersity of the LC droplets include flow rates and surface wettability. Under appropriate experimental conditions (i.e., when the surface is glass and the flow rate is sufficiently high), the LC droplets can be lifted off completely and carried away by the solution, forming free LC droplets (15-62 μm in diameter). These free LC droplets can respond to a chemical reaction and change their optical textures uniformly.

Multiprotein microcontact printing with micrometer resolution

Depositing multiple proteins on the same substrate in positions similar to the natural cellular environment is essential to tissue engineering and regenerative medicine. In this study, the development and verification of a multiprotein microcontact printing (μCP) technique is described. It is shown that patterns of multiple proteins can be created by the sequential printing of proteins with micrometer precision in registration using an inverted microscope. Soft polymeric stamps were fabricated and mounted on a microscope stage while the substrate to be stamped was placed on a microscope objective and kept at its focal distance. This geometry allowed for visualization of patterns during the multiple stamping events and facilitated the alignment of multiple stamped patterns. Astrocytes were cultured over stamped lane patterns and were seen to interact and align with the underlying protein patterns.

Fabricating protein immunoassay arrays on nitrocellulose using dip-pen lithography techniques

Advancements in lithography methods for printing biomolecules on surfaces are proving to be potentially beneficial for disease screening and biological research. Dip-pen nanolithography (DPN) is a versatile micro and nanofabrication technique that has the ability to produce functional biomolecule arrays. The greatest advantage, with respect to the printing mechanism, is that DPN adheres to the sensitive mild conditions required for biomolecules such as proteins. We have developed an optimised, high-throughput printing technique for fabricating protein arrays using DPN. This study highlights the fabrication of a prostate specific antigen (PSA) immunoassay detectable by fluorescence. Spot sizes are typically no larger than 8 μm in diameter and limits of detection for PSA are comparable with a commercially available ELISA kit. Furthermore, atomic force microscopy (AFM) analysis of the array surface gives great insight into how the nitrocellulose substrate functions to retain protein integrity. This is the first report of protein arrays being printed on nitrocellulose using the DPN technique and the smallest feature size yet to be achieved on this type of surface. This method offers a significant advance in the ability to produce dense protein arrays on nitrocellulose which are suitable for disease screening using standard fluorescence detection.

Modification of microneedles using inkjet printing

In this study, biodegradable acid anhydride copolymer microneedles containing quantum dots were fabricated by means of visible light dynamic mask micro-stereolithography-micromolding and inkjet printing. Nanoindentation was performed to obtain the hardness and the Young's modulus of the biodegradable acid anhydride copolymer. Imaging of quantum dots within porcine skin was accomplished by means of multiphoton microscopy. Our results suggest that the combination of visible light dynamic mask micro-stereolithography-micromolding and inkjet printing enables fabrication of solid biodegradable microneedles with a wide range of geometries as well as a wide range of pharmacologic agent compositions.

Quantitative analysis of serum procollagen type I C-terminal propeptide by immunoassay on microchip

Background

Sandwich enzyme-linked immunosorbent assay (ELISA) is one of the most frequently employed assays for clinical diagnosis, since this enables the investigator to identify specific protein biomarkers. However, the conventional assay using a 96-well microtitration plate is time- and sample-consuming, and therefore is not suitable for rapid diagnosis. To overcome these drawbacks, we performed a sandwich ELISA on a microchip.

Methods and Findings

The microchip was made of cyclic olefin copolymer with straight microchannels that were 300 µm wide and 100 µm deep. For the construction of a sandwich ELISA for procollagen type I C-peptide (PICP), a biomarker for bone formation, we used a piezoelectric inkjet printing system for the deposition and fixation of the 1st anti-PICP antibody on the surface of the microchannel. After the infusion of the mixture of 2.0 µl of peroxidase-labeled 2nd anti-PICP antibody and 0.4 µl of sample to the microchannel and a 30-min incubation, the substrate for peroxidase was infused into the microchannel; and the luminescence intensity of each spot of 1st antibody was measured by CCD camera. A linear relationship was observed between PICP concentration and luminescence intensity over the range of 0 to 600 ng/ml (r² = 0.991), and the detection limit was 4.7 ng/ml. Blood PICP concentrations of 6 subjects estimated from microchip were compared with results obtained by the conventional method. Good correlation was observed between methods according to simple linear regression analysis (R² = 0.9914). The within-day and between-days reproducibilities were 3.2–7.4 and 4.4–6.8%, respectively. This assay reduced the time for the antigen-antibody reaction to 1/6, and the consumption of samples and reagents to 1/50 compared with the conventional method.

Conclusion

This assay enabled us to determine serum PICP with accuracy, high sensitivity, time saving ability, and low consumption of sample and reagents, and thus will be applicable to clinic diagnosis.

Application of inkjet printing technique for biological material delivery and antimicrobial assays

A modified commercial inkjet printer was developed to deliver biological samples. The active Escherichia coli cells were directly printed at precisely targeted positions on agar-coated substrates via this technique to generate complex bacterial colony patterns. Viable cell arrays with a high density of 400 dots/cm(2) were obtained without the addition of any surfactants or other chemicals. Moreover, an applicable example of multiple-layer inkjet printing technique was adapted to deposit bacteria and antibiotics for antimicrobial potential assays. After fluorescent E. coli cells were printed, gradient concentrations of water-soluble antibiotics were ejected onto them to determine its minimum inhibitory concentration (MIC) to test the antimicrobial activities. This approach simplifies the experimental manipulation by replacing laborious manual loading processes with automatically controlled printing procedures, which makes it a versatile tool for high-throughput applications.

A printed nanolitre-scale bacterial sensor array

The last decade has witnessed a significant increase in interest in whole-cell biosensors for diverse applications, as well as a rapid and continuous expansion of array technologies. The combination of these two disciplines has yielded the notion of whole-cell array biosensors. We present a potential manifestation of this idea by describing the printing of a whole-cell bacterial bioreporters array. Exploiting natural bacterial tendency to adhere to positively charged abiotic surfaces, we describe immobilization and patterning of bacterial "spots" in the nanolitre volume range by a non-contact robotic printer. We show that the printed Escherichia coli-based sensor bacteria are immobilized on the surface, and retain their viability and biosensing activity for at least 2 months when kept at 4 °C. Immobilization efficiency was improved by manipulating the bacterial genetics (overproducing curli protein), the growth and the printing media (osmotic stress and osmoprotectants) and by a chemical modification of the inanimate surface (self-assembled layers of 3-aminopropyl-triethoxysilane). We suggest that the methodology presented herein may be applicable to the manufacturing of whole-cell sensor arrays for diverse high throughput applications.

Fabrication and characterization of a sialoside-based carbohydrate microarray biointerface for protein binding analysis with surface plasmon resonance imaging

Monitoring multiple biological interactions in a multiplexed array format has numerous advantages. However, converting well-developed surface chemistry for spectroscopic measurements to array-based high-throughput screening is not a trivial process and often proves to be the bottleneck in method development. This paper reports the fabrication and characterization of a new carbohydrate microarray with synthetic sialosides for surface plasmon resonance imaging (SPRi) analysis of lectin-carbohydrate interactions. Contact printing of functional sialosides on neutravidin-coated surfaces was carried out and the properties of the resulting elements were characterized by fluorescence microscopy and atomic force microscopy (AFM). Sambucus nigra agglutinin (SNA) was deposited on four different carbohydrate functionalized surfaces and differential binding was analyzed to reveal affinity variation as a function of headgroup sialic acid structures and linking bonds. SPRi studies indicated that this immobilization method could result in high quality arrays with RSD < 5% from array element to array element, superior to the conventional covalent linkage used for protein cholera toxin (CT) in a comparison experiment, which yields nonuniform array elements with RSD > 15%. Multiplexed detection of SNA/biotinylated sialoside interactions on arrays up to 400 elements has been performed with good data correlation, demonstrating the effectiveness of the biotin-neutravidin-based biointerface to control probe orientation for reproducible and efficient protein binding to take place. Additionally, the regeneration of the array surface was demonstrated with a glycine stripping buffer, rendering this interface reusable. This in-depth study of array surface chemistry offers useful insight into experimental conditions that can be optimized for better performance, allowing many different protein-based biointeractions to be monitored in a similar manner.

Nanoscale patterns of oligonucleotides formed by electrohydrodynamic jet printing with applications in biosensing and nanomaterials assembly

The widespread use of DNA in microarrays for applications in biotechnology, combined with its promise in programmed nanomaterials assembly, unusual electronic devices, and other areas has created interest in methods for patterning DNA with high spatial resolution. Techniques based on thermal or piezoelectric inkjet printing are attractive due to their noncontacting nature and their compatibility with diverse materials and substrate types; their modest resolution (i.e., 10-20 microm) represents a major limitation for certain systems. Here we demonstrate the use of an operationally similar printing approach that exploits electrohydrodynamic forces, rather than thermal or acoustic energy, to eject DNA inks through fine nozzles, in a controlled fashion. This DNA printer is capable of resolution approaching 100 nm. A range of experiments on patterns of DNA formed with this printer demonstrates its key features. Example applications in DNA-directed nanoparticle assembly and DNA aptamer-based biosensing illustrate two representative uses of the patterns that can be formed.

Bio-Microarray Fabrication Techniques—A Review

Microarrays with biomolecules (e.g., DNA and proteins), cells, and tissues immobilized on solid substrates are important tools for biological research, including genomics, proteomics, and cell analysis. In this paper, the current state of microarray fabrication is reviewed. According to spot formation techniques, methods are categorized as "contact printing" and "non-contact printing." Contact printing is a widely used technology, comprising methods such as contact pin printing and microstamping. These methods have many advantages, including reproducibility of printed spots and facile maintenance, as well as drawbacks, including low-throughput fabrication of arrays. Non-contact printing techniques are newer and more varied, comprising photochemistry-based methods, laser writing, electrospray deposition, and inkjet technologies. These technologies emerged from other applications and have the potential to increase microarray fabrication throughput; however, there are several challenges in applying them to microarray fabrication, including interference from satellite drops and biomolecule denaturization.

Silica Colloidal Crystals for Enhanced Fluorescence Detection in Microarrays

Silica colloidal crystals were investigated for their potential as high surface area materials to enhance sensitivity over planar surfaces for microarrays using fluorescence detection. A relation was derived showing how crystal thickness and transmission, as well as colloid size, combine to determine the optically accessible surface area for enhancing sensitivity. Experimentally, crystals of 250-nm colloids were prepared with thicknesses determined by SEM to be 1.6, 4.2, and 11.0 microm. The material was sintered at 1000 degrees C to make it durable without affecting the crystalline structure, as confirmed by SEM. UV/visible spectrometry showed the depth of penetration (1/e) to be 8.4 microm at 488 nm for these materials. Fluorescein-labeled streptavidin and biotin were used as a model ligand-receptor pair. For the fluorescence measurements, biotin was covalently bonded to the silica surfaces, and the fluorescence was detected from the captured streptavidin-fluorescein. The observed fluorescence enhancement agreed well with the theory developed here. Compared to a planar surface, the colloidal crystal of 11.0 microm in thickness enhanced the fluorescence by nearly a factor of 80, with only a 0.3% increase in fluorescence background.

Development of an Ultra-micro Sample Injector for Gas Chromatography Using an Ink-jet Microchip

An ultra-micro sample injector for gas chromatography (GC) was developed. An ink-jet microchip, originally used for industrial recorder, was modified at the edge near to an orifice, and fixed into the GC. In order to evaluate the characteristics of this injector, a sample injector and a thermal conductive detector (TCD) were connected directly, while water was used as the test sample. The volume of the droplet, the interval time and the back-pressure to the ink-jet microchip were investigated. Within the range of 1 - 5 nL volume injected sample, the TCD response according to the amount of the sample volume (the volume of one droplet from the ink-jet microchip was about 1 nL) was obtained. A good reproducibility of the peak area was obtained to be about 1.0% of the RSD value. In order to compare the injection method of the ink-jet chip with that using a micro-syringe, the method using the ink-jet chip could introduce 1/1000 of the amount of the sample and gave reproducible results.

Electrohydrodynamic generation and delivery of monodisperse picoliter droplets using a poly(dimethylsiloxane) microchip

We developed a drop-on-demand microdroplet generator for the discrete dispensing of biosamples into a bioanalytical unit. This disposable PDMS microfluidic device can generate monodisperse droplets of picoliter volume directly out of a plane sidewall of the microfluidic chip by an electrohydrodynamic mechanism. The droplet generation was accomplished without using either an inserted capillary or a monolithically built-in tip. The minimum droplet volume was approximately 4 pL, and the droplet generation was repeatable and stable for at least 30 min, with a typical variation of less than 2.0% of drop size. The Taylor cone, which is usually observed in electrospray, was suppressed by controlling the surface wetting property of the PDMS device as well as the surface tension of the sample liquids. A modification of the channel geometry right before the opening of the microchannel also enhanced the continuous droplet generation without applying any external pumping. A simple numerical simulation of the droplet generation verified the importance of controlling the surface wetting conditions for the droplet formation. Our microdroplet generator can be effectively applied to a direct interface of a microfluidic chip to a biosensing unit, such as AMS, MALDI-MS or protein microarray-type biochips.

DNA microarraying on compact disc surfaces. Application to the analysis of single nucleotide polymorphisms in Plum pox virus

The potential of using compact discs as high throughput screening platforms for DNA microarraying is discussed and applied to discriminate genetic variations of Plum pox virus.

Spraying Enzymes in Microemulsions of AOT in Nonpolar Organic Solvents for Fabrication of Enzyme Electrodes

A new technique suitable for automated, large-scale fabrication of enzyme electrodes by air-spraying enzymes in organic inks is presented. Model oxidoreductases, tyrosinase (Tyr) and glucose oxidase (GOx), were adapted to octane-based ink by entrapment in a system of reverse micelles (RM) of surfactant AOT in octane to separate and stabilize the catalytically active forms of the enzymes in nonpolar organic media. Nonpolar caoutchouk polymer was also used to create a kind of "dry micelles" at the electrode/solution interface. Enzyme/RM/polymer-containing organic inks were air-brushed onto conductive supports and were subsequently covered by sprayed Nafion membranes. The air-brushed enzyme electrodes exhibited relevant bioelectrocatalytic activity toward catechol and glucose, with a linear detection range of 0.1-100 microM catechol and 0.5-7 mM glucose; the sensitivities were 2.41 A M(-1) cm(-2) and 2.98 mA M(-1) cm(-2) for Tyr and GOx electrodes, respectively. The proposed technique of air-brushing enzymes in organic inks enables automated construction of disposable enzyme electrodes of various designs on a mass-production scale.

Development of a Microfluidic Platform with an Optical Imaging Microarray Capable of Attomolar Target DNA Detection

In this paper, DNA hybridization in a microfluidic manifold is performed using fluorescence detection on a fiber-optic microarray. The microfluidic device integrates optics, sample transport, and fluidic interconnects on a single platform. A high-density optical imaging fiber array containing oligonucleotide-labeled microspheres was developed. DNA hybridization was observed at concentrations as low as 10 aM with response times of less than 15 min at a flow rate of 1 microL/min using 50 microL of target DNA samples. The fast response times coupled with the low sample volumes and the use of a high-density, fiber-optic microarray format make this method highly advantageous. This paper describes the initial development, optimization, and integration of the microfluidic platform with imaging fiber arrays.