Volume 33, Issue 3

Among all the detection methods developed for bioassays, optical-based approaches are the most popular techniques. A widely used and accepted bioanalytical technique for routine characterization of molecular recognition events at a solid interface is surface plasmon resonance (SPR) spectroscopy. Compared with other techniques, SPR offers a series of advantages including rapid and real-time analysis, in situ detection, and the possibility to determine kinetic as well as thermodynamic parameters of interacting partners without the requirement of tagging one of the two partners. This method is nowadays used in academic and industrial research laboratories for drug discovery processes, safety, and quality control applications as well as for understanding bioaffinity reactions. Past studies have shown that SPR can detect approximately 100 ng/l of proteins. Currently, much effort is still invested to further improve SPR with respect to the sensitivity in the detection of low molecular weight analytes as well as in the detection limit for different analyte/ligand reactions. This review will focus on the use of gold nanoparticles as an amplification strategy in SPR sensing. Compared to other review articles highlighting the several synthetic routes and properties of gold nanoparticles and research utilizing gold nanoparticles for various sensing strategies, this review will exclusively look at the impact of gold nanostructures for ultrasensitive SPR sensing. Signal enhancement by gold nanoparticles is caused by several effects such as surface mass increase due to enhanced surface area, larger refractive index changes by the particle mass, themselves, and electromagnetic field coupling between the plasmonic properties of the particles (localized surface plasmon resonance) and propagating plasmons. The unique optical, electronic, and catalytic properties of gold nanoparticles put them into the forefront of interest for signal amplification as will be outlined here.

Soluble nanoscale lipid bilayers, termed nanodiscs, are widely used in science for studying the membrane-anchored and integral membrane protein complexes under defined experimental conditions. Although their formation occurs by a self-assembly process, nanodisc purification and the verification of proper reconstitution are still major challenges during the sample preparation. This review gives an overview of the methods used for purifying and analyzing nanodiscs and nanodisc-reconstituted membrane proteins, with an emphasis on the chromatographic and electrophoretic approaches.

Voltammetric and amperometric methods for screening compounds of pharmacological interest are reviewed on the basis of the types of electrodes and analytical strategies. The scope of conventional voltammetric and amperometric methods has been considerably expanded in the last years due to the development of a plethora of modified electrodes, in particular, those involving nanocomposites. The application of solid state voltammetric techniques for pharmacological screening has been also reviewed.

DNAzymes are a series of functional oligonucleotides obtained through in vitro selection and able to catalyze the reaction of substrates with the help of some special cofactors such as metal ions, L-histidine and hemin. Compared with naturally occurring bio-enzymes, DNAzymes are more stable and amenable to modification and preparation. Due to their outstanding properties, DNAzymes have been widely used in biological applications, such as target detection and signal amplification. Nanomaterials, with special characteristics including quantum size effect, high biocompatibility, large surface-to-volume ratio and overall structural robustness, exhibit important application prospects in nanotechnology. By combining with a variety of nanomaterials, DNAzyme achieves a lot of special applications in biochemistry. This review summarizes recent achievements in the field of DNAzyme-conjugated nanomaterials for biosensing applications. For a brief demonstration, nanomaterials including gold nanoparticles, carbon nanomaterials, magnetic nanoparticles and semiconductor quantum dots are taken as examples.