The analysis of biomolecular interactions is key in the drug development process. Label-free biosensor methods provide information on binding, kinetics, concentration, and the affinity of an interaction. These techniques provide real-time monitoring of interactions between an immobilized ligand (such as a receptor) to an analyte in solution without the use of labels. Advances in biosensor design and detection using BioLayer Interferometry (BLI) provide a simple platform that enables label-free monitoring of biomolecular interactions without the use of flow cells. We review the applications of BLI in a wide variety of research and development environments for quantifying antibodies and proteins and measuring kinetics parameters.

Nanowires are commonly used as tools for interfacing living cells, acting as biomolecule-delivery vectors or electrodes. It is generally assumed that the small size of the nanowires ensures a minimal cellular perturbation, yet the effects of nanowires on cell migration and proliferation remain largely unknown. Fibroblast behaviour on vertical nanowire arrays is investigated, and it is shown that cell motility and proliferation rate are reduced on nanowires. Fibroblasts cultured on long nanowires exhibit failed cell division, DNA damage, increased ROS content and respiration. Using focused ion beam milling and scanning electron microscopy, highly curved but intact nuclear membranes are observed, showing no direct contact between the nanowires and the DNA. The nanowires possibly induce cellular stress and high respiration rates, which trigger the formation of ROS, which in turn results in DNA damage. These results are important guidelines to the design and interpretation of experiments involving nanowire-based transfection and electrical characterization of living cells.

Techniques to detect and quantify DNA and RNA molecules in biological samples have played a central role in genomics research1–3. Over the past decade, several techniques have been developed to improve detection performance and reduce the cost of genetic analysis4–10. In particular, dramatic advances in label-free methods have been reported11–17. Yet, detection of DNA molecules at concentrations below femtomolar level requires amplified detection schemes1,8. Here we report a unique nanomechanical response of hybridized DNA and RNA molecules that serves as an intrinsic molecular label. Nanomechanical measurements on a microarray surface exhibit excellent background signal rejection that allows direct detection and counting of hybridized molecules. The digital response of the sensor provides a large dynamic range that is critical for gene expression profiling. We have measured differential expressions of miRNAs in tumor samples, which has been shown to help discriminate tissue origins of metastatic tumors18. 200 picograms of total RNA is found to be sufficient for this analysis. In addition, the limit of detection in pure samples is found to be 1 attomolar. These results suggest that nanomechanical readout of microarrays promises attomolar level sensitivity and large dynamic range for the analysis of gene expression, while eliminating biochemical manipulations, amplification, and labeling.

With a view to the miniaturization of ion-selective electrodes (ISEs), thin (10−20 μm) polymer membranes are directly contacted to Au covered with a redox-active, lipophilic self-assembled monolayer (SAM). Several homogeneous and mixed monolayers are characterized by reflection−absorption infrared spectroscopy, ellipsometry, scanning tunneling microscopy, cyclic voltammetry, and contact angle measurements. These Au/thiol surfaces are combined with different K+-selective sensing membranes based on poly(vinyl chloride) (PVC), polyurethane (PUR), or PVC/PUR blends as a matrix and valinomycin as an ionophore. The sensors are investigated with regard to their potential stability in the presence of O2 and redox-active species. The occurrence of potential drifts upon changing the conditioning KCl solution to a NaCl solution is used as an indicator for the formation of an aqueous film between the membrane and Au/SAM. Stable systems are obtained with mixed monolayers (advancing contact angle θa ≈ 83°) and PVC membranes with a lower than usual plasticizer content (33 wt %), the ternary systems PVC/PUR/plasticizer (1:1:1), and PUR with 33 wt % plasticizer. On the other hand, a water film is formed between Au/SAM and conventional PVC membranes having 66% plasticizer and with less lipophilic monolayers uniquely based on a redox-active compound (θa ≈ 70°). The new solid-contact ISEs are promising both for miniaturization and for improving lower detection limits.