Fortifying the diagnostic-frontiers with nanoscale technology amidst the COVID-19 catastrophe

The power of the small has been realized time and again in human history. The recent global fiasco, COVID-19, interlaced with unprecedented biomedical consequences and human loss, modifications in nutritional habits and physical activity, as well as tremendous impacts on economic, political, social, and psychophysiological health status [1,2], ushered in by the ‘petite yet powerful’ and ‘biochemically and genetically guileful’ SARS-CoV-2 [3] testifies the veracity of the statement. Amidst the global race to discover antiviral agents, neutralizing antibodies, and safe and effective vaccines [3,4], the denigration faced by governments of different countries for the deplorable mass testing efficiency, scarcity of sufficient testing kits as well as the asymptomatic viral transmission (manifested as the Achilles’ heel amidst the containment strategies) project the expansion and upscaling of prompt, sensitive, and effective SARS-CoV-2 testing strategies, executed in a well-timed, tactical, and regular mode as a focal global requisite. The current detection approaches for COVID-19 relies on clinical characteristics, epidemiological history, chest imaging, and laboratory diagnosis [5]. Thus, this write up aims to present a highlight of the current endeavors and progress in harnessing nanoscalebased diagnostic technology vis-à-vis the various pros and cons of the generic approaches for COVID-19 detection. At this juncture, one may easily perceive the fact that a clear understanding of the genomic and the proteomic makeup of the pathogen as well as the alterations in the proteins/genes’ expression pattern in the host during and post-infection is a pre-requisite for the development of advanced diagnostic platforms including nano-based techniques. Similar to other coronaviruses, SARS-CoV-2 possesses a positive-sense single-stranded genomic RNA (with a 5′-cap and a 3′-poly(A) tail), approximately 30 kb in length [6]. Transcriptional regulatory sequences (TRSs) precede the 14 open reading frames (ORFs) in its genome; at the 3′ end, four structural proteins (spike, envelope, membrane, nucleocapsid) are encoded while nine putative ORFs for accessory factors intersperse the structural genes [6]. On a note of pertinence, the invitation to the virus into human cells is placed by the human angiotensin-converting enzyme 2 (ACE2) (expressed in a plethora of cells and tissues) that interacts with the receptor-binding domains (RBD) of the spike (S) glycoprotein [4,6]. In fact, coronaviruses represent one of the few RNA viruses, endowed with genomic proofreading potency and a deadly dynamism, marked by frequent swapping of RNA chunks between distant coronavirus relatives, resulting in intimidating versions or mutants with the capacity to infect new cell types and jump across species [7]. The molecular backdrop of the host–pathogen interaction, the immunological aspects, and the pathophysiology of the disease are gradually unfolding, besides various biomarkers, associated with COVID-19 have been identified [8], thereby, opening avenues for expanding the diagnostic frontiers. Having said that, the initial screening and identification of SARS-CoV-2, the viral etiology of COVID-19 relied on the concert of computed tomography-based imaging/detection of the radiological changes in the lungs (within 1–2 h, though marked with low sensitivity), whole genome sequencing and electron microscopic visualization of the virus particles. The high cost, the requirement of high viral burden, expertise in viral recognition and the labor-intensive nature of the latter needs no elaboration. On the other hand, viral culture aids in the isolation of many viruses for subsequent research, however, prolonged time consumption (2–3 days), biosafety concerns as well as the requirement of expertise for maintenance of cell cultures and interpretation of characteristic cytopathic effects are the major challenges. Amongst others, the molecular detection techniques [5] for SARS-CoV-2 encompass RTPCR and different nucleic acid-based techniques including nucleic acid sequence-based amplification (NASBA) and loopmediated isothermal amplification (LAMP). Albeit, the selectivity and sensitivity of the conventional real-time RT-PCR are well established, howbeit, the requisite of trained personnel, accessibility of large and expensive instruments and reagents in specific laboratory settings, and time-intensive attribute pose serious feasibility constraints in environments with limited resources. Failure to identify recovered patients with past infection, chances of failed amplification due to inhibitors, and the possibility of false-negative results due to genetic variability are challenges for both conventional (turn-around-time, TAT: 3–4 hours) and sample-to-answer type real-time RT-PCR (TAT < 1 h) approaches. Techniques such as nanopore target sequencing (NTS) (based on the concert of target amplification