Low-Cost Optical Assays for Point-of-Care Diagnosis in Resource-Limited Settings.

Readily deployable, low-cost point-of-care medical devices such as lateral flow assays (LFAs), microfluidic paper-based analytical devices (µPADs), and microfluidic thread-based analytical devices (µTADs) are urgently needed in resource-poor settings. Governed by the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free, and deliverability) set by the World Health Organization, these reliable platforms can screen a myriad of chemical and biological analytes including viruses, bacteria, proteins, electrolytes, and narcotics. The Ebola epidemic in 2014 and the ongoing pandemic of SARS-CoV-2 have exemplified the ever-increasing importance of timely diagnostics to limit the spread of diseases. This review provides a comprehensive survey of LFAs, µPADs, and µTADs that can be deployed in resource-limited settings. The subsequent commercialization of these technologies will benefit the public health, especially in areas where access to healthcare is limited.

Paper-based electrochemical biosensor for diagnosing COVID-19: Detection of SARS-CoV-2 antibodies and antigen.

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is emerging as a global pandemic outbreak. To date, approximately one million deaths and over 32 million cases have been reported. This ongoing pandemic urgently requires an accurate testing device that can be used in the field in a fast manner. Serological assays to detect antibodies have been proven to be a great complement to the standard method of reverse transcription-polymerase chain reaction (RT-PCR), particularly after the second week of infection. We have developed a specific and sensitive immunosensor for immunoglobulin detection produced against SARS-CoV-2. Unlike other lateral flow-based assays (LFAs) involving the utilization of multiple antibodies, we have reported a label-free paper-based electrochemical platform targeting SARS-CoV-2 antibodies without the specific requirement of an antibody. The presence of SARS-CoV-2 antibodies will interrupt the redox conversion of the redox indicator, resulting in a decreased current response. This electrochemical sensor was proven effective in real clinical sera from patients with satisfactory results. In addition, the proposed format was also extended to antigen detection (the spike protein of SARS-CoV-2), which presents new possibilities for diagnosing COVID-19.