Nanopipettes-The past and the present

Nanopipettes, characterized by nanoscale sized pores and simple fabrication techniques, are of increasing scientific interest due to their application in a variety of fields, including analytical chemistry, nanophysiology, molecular diagnostics, and cellular biology. Nanopipettes have been extensively used for the development of electrochemical biosensors, as they offer the combined advantage of nanoscale dimensions and the selectivity and sensitivity of conventional solid-state biosensors. Over the years, with advances in technology and the expansion of research interests, functionalized nanopipettes have been successfully employed for performing real-time quantitative measurement of changes within a single cell. They have also been routinely used to aspirate/inject attoliter to picoliter volumes at intracellular levels and have become the "go-to" tools for cutting-edge research in molecular and cell biology. The use of nanopipettes as probes for imaging soft materials through scanning probe microscope (SPM) techniques such as scanning electrochemical microscopy and scanning ion-conductance microscopy has been widely explored. Advances in both the technical and theoretical aspects of nanopipette technology have a profound impact on early diagnosis and treatment of various diseases including cancer, diabetes, and Alzheimer's. In this review, we provide insights into the fabrication, morphological, and electrochemical characterization of the nanopipette and comprehensively discuss the various applications available in the literature of nanopipettes as sensing probes, monitoring probes for single cells, and SPMs.