Strategies for the Development of Metallic-Nanoparticle-Based Label-Free Biosensors and Their Biomedical Applications

Label-free biosensors offer accurate sensing capabilities due to the reliable quantification of biological and biochemical processes. These devices function by establishing a dynamic interaction of analyte and receptor molecules and convert this interaction into a measurable signal through a transducer. In recent decades, label-free biosensors have attracted attention in biomedical applications due to the ease of linking nanomaterials with bioreceptor molecules. In this review, recent advances in sensitivity, specificity, and sensing mechanism related to label-free biosensors of metallic nanoparticles of gold, silver, aluminium, copper, and zinc oxide are presented. Selected sensing methods based on fluorescence, surface plasmon resonance, surface-enhanced Raman scattering, metal-enhanced fluorescence, and electrochemical sensors are discussed. New measurement techniques and rapid progress of label-free biosensors are going to play a vital role in the real-time detection of biomarkers in clinical samples, such as blood plasma, serum, and urine, as well as in targeted drug delivery. Future trends of these label-free biosensing mechanisms and their development are also discussed.