Equilibrium and dynamic design principles for binding molecules engineered for reagentless biosensors

Leaky waveguide biosensors for label-free measurement of human serum albumin

Early diagnosis of diseases such as kidney disease relies on the successful measurement of albumin concentration in urine. We report label-free detection of human serum albumin (HSA) using a leaky waveguide (LW) optical biosensor. The LW reported in this work comprised a few microns-thick mesoporous polyacrylamide hydrogel film deposited on a glass substrate by casting and, for the first time, copolymerized with N-(3-aminopropyl)methacrylamide (APMAA) to provide functional amine groups required to immobilise recognition elements, half-antibody fragments. Furthermore, this is an unprecedented report on the use of a high molecular weight (3700 D) poly(ethylene glycol) diacrylamide in contrast to previously reported low molecular weight bis-acrylamide crosslinkers to increase the porosity of waveguide films. Equally, other parameters such as molar ratio of APMAA to acrylamide and total weight of (monomers and crosslinker) to volume ratio were optimised to obtain hydrogel films with pore size and amine groups required to immobilise half-antibody fragments in hydrogel films. Three different strategies for immobilisation of recognition elements; two based on streptavidin biotin interactions and the third based on half fragments of antibody were studied. The third immobilisation strategy resulted in the most reproducible results and hence was used to measure the equilibrium dissociation constant of HSA and its corresponding half-antibody fragments. Using the LW-based label-free optical biosensor, HSA was successfully detected with a limit of detection of 28 ng mL-1 in buffer and the lowest concentration of HSA measured in this work was 66.5 ng mL-1. This capability of quantitation of HSA by the LW can be built upon to realise a LW biosensor for early detection of diseases including kidney disease.

Liver-on-a-Chip Integrated with Label-Free Optical Biosensors for Rapid and Continuous Monitoring of Drug-Induced Toxicity

Drug toxicity assays using conventional 2D static cultures and animal studies have limitations preventing the translation of potential drugs to the clinic. The recent development of organs-on-a-chip platforms provides promising alternatives for drug toxicity/screening assays. However, most studies conducted with these platforms only utilize single endpoint results, which do not provide real-time/ near real-time information. Here, a versatile technology is presented that integrates a 3D liver-on-a-chip with a label-free photonic crystal-total internal reflection (PC-TIR) biosensor for rapid and continuous monitoring of the status of cells. This technology can detect drug-induced liver toxicity by continuously monitoring the secretion rates and levels of albumin and glutathione S-transferase α (GST-α) of a 3D liver on-a-chip model treated with Doxorubicin. The PC-TIR biosensor is based on a one-step antibody functionalization with high specificity and a detection range of 21.7 ng mL-1 to 7.83 x 103 ng mL-1 for albumin and 2.20 ng mL-1 to 7.94 x 102 ng mL-1 for GST-α. This approach provides critical advantages for the early detection of drug toxicity and improved temporal resolution to capture transient drug effects. The proposed proof-of-concept study introduces a scalable and efficient plug-in solution for organ-on-a-chip technologies, advancing drug development and in vitro testing methods by enabling timely and accurate toxicity assessments.

Design Principles for SuCESsFul Biosensors: Specific Fluorophore/Analyte Binding and Minimization of Fluorophore/Scaffold Interactions

Quantifying protein location and concentration is critical for understanding function in situ. Scaffold conjugated to environment-sensitive fluorophore (SuCESsFul) biosensors, in which a reporting fluorophore is conjugated to a binding scaffold, can, in principle, detect analytes of interest with high temporal and spatial resolution. However, their adoption has been limited due to the extensive empirical screening required for their development. We sought to establish design principles for this class of biosensor by characterizing over 400 biosensors based on various protein analytes, binding proteins, and fluorophores. We found that the brightest readouts are attained when a specific binding pocket for the fluorophore is present on the analyte. Also, interaction of the fluorophore with the binding protein it is conjugated to can raise background fluorescence, considerably limiting sensor dynamic range. Exploiting these two concepts, we designed biosensors that attain a 100-fold increase in fluorescence upon binding to analyte, an order of magnitude improvement over the previously best-reported SuCESsFul biosensor. These design principles should facilitate the development of improved SuCESsFul biosensors.

Receptor-ligand interactions: Advanced biomedical applications

Receptor-ligand interactions (RLIs) are at the base of all biological events occurring in living cells. The understanding of interactions between complementary macromolecules in biological systems represents a high-priority research area in bionanotechnology to design the artificial systems mimicking natural processes. This review summarizes and analyzes RLIs in some cutting-edge biomedical fields, in particular, for the preparation of novel stationary phases to separate complex biological mixtures in medical diagnostics, for the design of ultrasensitive biosensors for identification of biomarkers of various diseases at early stages, as well as in the development of innovative biomaterials and approaches for regenerative medicine. All these biotechnological fields are closely related, because their success depends on a proper choice, combination and spatial disposition of the single components of ligand-receptor pairs on the surface of appropriately designed support.