Process-property correlations in laser-induced graphene electrodes for electrochemical sensing.

Laser-induced graphene (LIG) has emerged as a promising electrode material for electrochemical point-of-care diagnostics. LIG offers a large specific surface area and excellent electron transfer at low-cost in a binder-free and rapid fabrication process that lends itself well to mass production outside of the cleanroom. Various LIG micromorphologies can be generated when altering the energy input parameters, and it was investigated here which impact this has on their electroanalytical characteristics and performance. Energy input is well controlled by the laser power, scribing speed, and laser pulse density. Once the threshold of required energy input is reached a broad spectrum of conditions leads to LIG with micromorphologies ranging from delicate irregular brush structures obtained at fast, high energy input, to smoother and more wall like albeit still porous materials. Only a fraction of these LIG structures provided high conductance which is required for appropriate electroanalytical performance. Here, it was found that low, frequent energy input provided the best electroanalytical material, i.e., low levels of power and speed in combination with high spatial pulse density. For example, the sensitivity for the reduction of K3[Fe(CN)6] was increased almost 2-fold by changing fabrication parameters from 60% power and 100% speed to 1% power and 10% speed. These general findings can be translated to any LIG fabrication process independent of devices used. The simple fabrication process of LIG electrodes, their good electroanalytical performance as demonstrated here with a variety of (bio)analytically relevant molecules including ascorbic acid, dopamine, uric acid, p-nitrophenol, and paracetamol, and possible application to biological samples make them ideal and inexpensive transducers for electrochemical (bio)sensors, with the potential to replace the screen-printed systems currently dominating in on-site sensors used.

Microfluidic-enabled magnetic labelling of nanovesicles for bioanalytical applications.

Bearing multiple functionalities dramatically increases nanomaterial capabilities to enhance analytical assays by improving sensitivity, selectivity, sample preparation, or signal read-out strategies. Magnetic properties are especially desirable for nanoparticles and nanovesicles as they assist in negating diffusion limitations and improving separation capabilities. Here, we propose a microfluidic method that reliably labels functional nanovesicles while avoiding the risk of crosslinking that would lead to large conglomerates as typically observed in bulk reactions. Thus, the carboxy groups of bi-functional biotinylated fluorescent liposomes were activated in bulk. They were then covalently bound to amino group presenting magnetic beads immobilized through a magnetic field within microfluidic channels. Microfluidic design and coupling strategy optimization led to a 62% coupling efficiency when using 1 µm magnetic beads. The yield dropped to 13% with 30 nm magnetic nanoparticles (MNPs) likely due to crowding of the MNPs on the magnet. Finally, both populations of these tri-functional liposomes were applied to a biological binding assay demonstrating their superior performance under the influence of a magnetic field. The microfluidic functionalization strategy lends itself well for massively parallelized production of larger volumes and can be applied to micro- and nanosized vesicles and particles.

Functional Nanomaterials and Nanostructures Enhancing Electrochemical Biosensors and Lab-on-a-Chip Performances: Recent Progress, Applications, and Future Perspective.

Electrochemical biosensors and associated lab-on-a-chip devices are the analytical system of choice when rapid and on-site results are needed in medical diagnostics and food safety, for environmental protection, process control, wastewater treatment, and life sciences discovery research among many others. A premier example is the glucose sensor used by diabetic patients. Current research focuses on developing sensors for specific analytes in these application fields and addresses challenges that need to be solved before viable commercial products can be designed. These challenges typically include the lowering of the limit of detection, the integration of sample preparation into the device and hence analysis directly within a sample matrix, finding strategies for long-term in vivo use, etc. Today, functional nanomaterials are synthesized, investigated, and applied in electrochemical biosensors and lab-on-a-chip devices to assist in this endeavor. This review answers many questions around the nanomaterials used, their inherent properties and the chemistries they offer that are of interest to the analytical systems, and their roles in analytical applications in the past 5 years (2013-2018), and it gives a quantitative assessment of their positive effects on the analyses. Furthermore, to facilitate an insightful understanding on how functional nanomaterials can be beneficial and effectively implemented into electrochemical biosensor-based lab-on-a-chip devices, seminal studies discussing important fundamental knowledge regarding device fabrication and nanomaterials are comprehensively included here. The review ultimately gives answers to the ultimate question: "Are they really needed or can bulk materials accomplish the same?" Finally, challenges and future directions are also discussed.