Innovative Quantification of Critical Quality Attributes

Potency testing is an important part of the evaluation of cellular therapy products. In vitro quantification of identified quality-related biomarkers is a technique often used at the laboratory. Nonetheless, the limited stability of most cellular therapy products, the lot variability and the limited time within which to perform testing are currently hindering their widespread use. Fortunately, within the last two decades, the evolution of material technology and miniaturisation processes has enabled the research community to shift the spotlight of attention towards the Lab-on-Chip concept for diagnostic applications. Such devices enable portable, rapid, sensitive, automated and affordable biochemical analyses aiming to advance the healthcare services across a broad application spectrum. However, it could be argued that the aspirations on their affordability are far from being exceeded, mainly due to the lack of a practical manufacturing technology. The Lab-on-Printed Circuit Board (Lab-on-PCB) approach has demonstrated enormous potential for developing economical diagnostic platforms leveraging the advantage provided by economy of scale manufacturing of the long-standing PCB industry. The integration capabilities that the PCB platform introduces to the Lab-on-Chip concept concerning the electronics and microfluidics seem to be unique. In this chapter, we will be reviewing the progress of Lab-on-PCB prototypes quantifying within miniaturised microchips a range of critical quality attributes with potential in potency testing. We will focus on their technology and applications whilst addressing the potential of this approach in practical use and commercialisation.

Biocompatibility Study of a Commercial Printed Circuit Board for Biomedical Applications: Lab-on-PCB for Organotypic Retina Cultures

Printed circuit board (PCB) technology is well known, reliable, and low-cost, and its application to biomedicine, which implies the integration of microfluidics and electronics, has led to Lab-on-PCB. However, the biocompatibility of the involved materials has to be examined if they are in contact with biological elements. In this paper, the solder mask (PSR-2000 CD02G/CA-25 CD01, Taiyo Ink (Suzhou) Co., Ltd., Suzhou, China) of a commercial PCB has been studied for retinal cultures. For this purpose, retinal explants have been cultured over this substrate, both on open and closed systems, with successful results. Cell viability data shows that the solder mask has no cytotoxic effect on the culture allowing the application of PCB as the substrate of customized microelectrode arrays (MEAs). Finally, a comparative study of the biocompatibility of the 3D printer Uniz zSG amber resin has also been carried out.

Utilising Commercially Fabricated Printed Circuit Boards as an Electrochemical Biosensing Platform

Printed circuit boards (PCBs) offer a promising platform for the development of electronics-assisted biomedical diagnostic sensors and microsystems. The long-standing industrial basis offers distinctive advantages for cost-effective, reproducible, and easily integrated sample-in-answer-out diagnostic microsystems. Nonetheless, the commercial techniques used in the fabrication of PCBs produce various contaminants potentially degrading severely their stability and repeatability in electrochemical sensing applications. Herein, we analyse for the first time such critical technological considerations, allowing the exploitation of commercial PCB platforms as reliable electrochemical sensing platforms. The presented electrochemical and physical characterisation data reveal clear evidence of both organic and inorganic sensing electrode surface contaminants, which can be removed using various pre-cleaning techniques. We demonstrate that, following such pre-treatment rules, PCB-based electrodes can be reliably fabricated for sensitive electrochemical biosensors. Herein, we demonstrate the applicability of the methodology both for labelled protein (procalcitonin) and label-free nucleic acid (E. coli-specific DNA) biomarker quantification, with observed limits of detection (LoD) of 2 pM and 110 pM, respectively. The proposed optimisation of surface pre-treatment is critical in the development of robust and sensitive PCB-based electrochemical sensors for both clinical and environmental diagnostics and monitoring applications.

Enzyme-assisted glucose quantification for a painless Lab-on-PCB patch implementation

In the context of an integrated Lab-on-PCB wearable patch extracting interstitial fluid from the patient via integrated microneedles, the requirements from the integrated biosensing part are quite special compared to static glucose electrochemical biosensors. Hence, in this study, a fully PCB-integrated enzymatic glucose quantification Lab-on-Chip device is presented and evaluated considering these special requirements for such a patch implementation: a) range and limit of detection compatible with interstitial fluid glucose levels of diabetic patients and b) effect of sample flow rate on the biosensing platform performance. This work employs a chronoamperometric approach for glucose detection based on covalently immobilized glucose oxidase on PCB-integrated electrodes. The chronoamperometric measurements show that this platform exhibits μM range sensitivity, high specificity, and good reproducibility, and the assay can detect glucose from 10 μM to 9 mM with a lower limit of detection of 10 μM. The demonstrated detection range under continuous flow proved compatible with interstitial fluid glucose levels of diabetic patients. The sample-to-answer time of our Lab-on-PCB device is less than 1 min (sample delivery of few seconds and 20 s for electrochemical measurement), employing sample volumes of 50 μL in this instance. Increased flow rates substantially improve the platform sensitivity (1.1 μA/mM @0 μL/min to 6.2 μA/mM @10 μL/min), with the measured current increasing exponentially to the flow rate, as opposed to the theoretically expected much lower dependence. This work demonstrates the feasibility of Lab-on-PCB patches in terms of biosensing performance, paving the way for the first cost-effective, painless diabetes management microsystem.

Modular Pressure and Flow Rate-Balanced Microfluidic Serial Dilution Networks for Miniaturised Point-of-Care Diagnostic Platforms

Fast, efficient and more importantly accurate serial dilution is a necessary requirement for most biochemical microfluidic-based quantitative diagnostic applications. Over the last two decades, a multitude of microfluidic devices has been proposed, each one demonstrating either a different type of dilution technique or complex system architecture based on various flow source and valving combinations. In this work, a novel serial dilution network architecture is demonstrated, implemented on two entirely different substrates for validation and performance characterisation. The single layer, stepwise serial diluter comprises an optimised microfluidic network, where identical dilution ratios per stage are ensured, either by applying equal pressure or equal flow rates at both inlets. The advantages of this serial diluter are twofold: Firstly, it is structured as a modular unit cell, simplifying the required fluid driving mechanism to a single source for both sample and buffer solution. Thus, this unit cell can be used as a fundamental microfluidic building block, forming multistage serial dilution cascades, once combined appropriately with itself or other similar unit cells. Secondly, the serial diluter can tolerate the inevitable flow source fluctuations, ensuring constant dilution ratios without the need to employ damping mechanisms, making it ideal for Point of Care (PoC) platforms. Proof-of-concept experiments with glucose have demonstrated good agreement between simulations and measurements, highlighting the validity of our serial diluter.

Biophysical measurement of red blood cells by laboratory on print circuit board chip

Microfluidic impedance pulse sensor has emerged as an easily handled and low-cost platform in the electrical analysis of biological cells. In the conventional method, impedance sensor demanded expensive patterning metal electrodes on the substrate, which are directly in touch with electrolytes in order to measure the microfluidic channel impedance change. In this article, a cost-effective microfluidic impedance sensor built upon a dielectric film coated printed circuit board is introduced. Impedance electrodes are protected by a dielectric film layer from electrochemical erosion between electrodes and electrolyte. Human red blood cells from adult and neonatal were utilized to demonstrate the feasibility of the proposed device in the electroanalysis of biological cells.

High-performance PCB-based capillary pumps for affordable point-of-care diagnostics

Capillary pumps are integral components of passive microfluidic devices. They can displace precise volumes of liquid, avoiding the need for external active components, providing a solution for sample preparation modules in Point-of-Care (PoC) diagnostic platforms. In this work, we describe a variety of high-performance capillary pump designs, suitable for the Lab-on-Printed-Circuit-Board technology (LoPCB). Pumps are fabricated entirely on Printed Circuit Board (PCB) substrates via commercially available manufacturing processes. We demonstrate the concept of LoPCB technology and detail the fabrication method of different architectures of PCB-based capillary pumps. The capillary pumps are combined with microfluidic channels of various hydraulic resistances and characterised experimentally for different micropillar shapes and minimum feature size. Their performance in terms of flow rate is reported. Due to the superhydrophilic properties of oxygen plasma treated FR-4 PCB substrate, the capillary pump flow rates are much higher (138 μL/min, for devices comprising micropillar arrays without preceding microchannel) than comparable devices based on glass, silicon or polymers. Finally, we comment on the technology's prospects, such as incorporating more complicated microfluidic networks that can be tailored for assays.

Amperometric IFN-γ immunosensors with commercially fabricated PCB sensing electrodes

Lab-on-a-Chip (LoC) technology has the potential to revolutionize medical Point-of-Care diagnostics. Currently, considerable research efforts are focused on innovative production technologies that will make commercial upscaling of lab-on-chip products financially viable. Printed circuit board (PCB) manufacturing techniques have several advantages in this field. In this paper we focus on transferring a complete IFN-γ enzyme-linked immune-sorbent assay (ELISA) onto a commercial PCB electrochemical biosensing platform, We adapted a commercially available ELISA to detect the enzyme product TMB/H2O2 using amperometry, successfully reproducing the colorimetry-obtained ELISA standard curve. The results demonstrate the potential for the integration of these components into an automated, disposable, electronic ELISA Lab-on-PCB diagnostic platform.

Surface and Electrical Characterization of Ag/AgCl Pseudo-Reference Electrodes Manufactured with Commercially Available PCB Technologies

Lab-on-Chip is a technology that could potentially revolutionize medical Point-of-Care diagnostics. Considerable research effort is focused towards innovating production technologies that will make commercial upscaling financially viable. Printed circuit board manufacturing techniques offer several prospects in this field. Here, we present a novel approach to manufacturing Printed Circuit Board (PCB)-based Ag/AgCl reference electrodes, an essential component of biosensors. Our prototypes were characterized both structurally and electrically. Scanning Electron Microscopy (SEM) and X-Ray Photoelectron Spectroscopy (XPS) were employed to evaluate the electrode surface characteristics. Electrical characterization was performed to determine stability and pH dependency. Finally, we demonstrate utilization along with PCB pH sensors, as a step towards a fully integrated PCB platform, comparing performance with discrete commercial reference electrodes.