Since their discovery almost three decades ago, DNAzymes have been used extensively in biosensing. Depending on the type of DNAzyme being used, these functional oligonucleotides can act as molecular recognition elements within biosensors, offering high specificity to their target analyte, or as reporters capable of transducing a detectable signal. Several parameters need to be considered when designing a DNAzyme-based biosensor. In particular, given that many of these biosensors immobilize DNAzymes onto a sensing surface, selecting an appropriate immobilization strategy is vital. Suboptimal immobilization can result in both DNAzyme detachment and poor accessibility toward the target, leading to low sensing accuracy and sensitivity. Various approaches have been employed for DNAzyme immobilization within biosensors, ranging from amine and thiol-based covalent attachment to non-covalent strategies involving biotin–streptavidin interactions, DNA hybridization, electrostatic interactions, and physical entrapment. While the properties of each strategy inform its applicability within a proposed sensor, the selection of an appropriate strategy is largely dependent on the desired application. This is especially true given the diverse use of DNAzyme-based biosensors for the detection of pathogens, metal ions, and clinical biomarkers. In an effort to make the development of such sensors easier to navigate, this paper provides a comprehensive review of existing immobilization strategies, with a focus on their respective advantages, drawbacks, and optimal conditions for use. Next, common applications of existing DNAzyme-based biosensors are discussed. Last, emerging and future trends in the development of DNAzyme-based biosensors are discussed, and gaps in existing research worthy of exploration are identified.

Promising nanotechnological platforms, based on inorganic nanoparticles and nanomaterials, have emerged in such fields as targeted drug delivery, bio- and chemical sensing, catalysis, antimicrobial coatings, and optoelectronic devices, among others. However, concerns regarding the sustainability of physicochemically-synthesized nanomaterials, which often require energy-intensive processes, high temperatures, toxic solvents or undesirable chemical wastes, have also emerged. Researchers have therefore looked to replace chemical syntheses by sustainable and environmentally friendly techniques. Biosynthesis of nanomaterials, i.e., the use of living organisms, their components, extracts or biomolecules, as catalysts for the sustainable production of nanomaterials, has experienced a tremendous expansion during the last two decades. Among these production platforms, the roles of algae have attracted increasing attention from research scientists worldwide. The aim of the present review, the first of its kind, is to provide important information to readers regarding the diversity of algal strains exploited in the booming field of nanobiotechnology and green chemistry, the various methodologies through which these diverse organisms are used, the variety of fabricated nanomaterials composed of noble metals, oxides and chalcogenides, and the significance of the large range of sizes and shapes of these nanomaterials that confer to them unique properties desirable for specific bio-applications.