The current approaches of diagnostic platforms for detecting SARS-CoV-2 infections mostly relied on adapting the existing technology. In this work, a simple and low-cost electrochemical sensing platform for detecting SAR-CoV-2 antigen was established. The proposed sensor combined the innovative disposable paper-based immunosensor and cost-effective plant-based anti-SARS-CoV-2 monoclonal antibody CR3022, expressed in Nicotiana benthamiana. The cellulose nanocrystal was modified on screen-printed graphene electrode to provide the abundant COOH functional groups on electrode surface, leading to the high ability for antibody immobilization. The quantification of the presence receptor binding domain (RBD) spike protein of SARS-CoV-2 was performed using differential pulse voltammetry by monitoring the changing current of [Fe(CN)₆]^3-/4- redox solution. The current change of [Fe(CN)₆]^3-/4- before and after the presence of target RBD could be clearly distinguished, providing a linear relationship with RBD concentration in the range from 0.1 pg/mL to 500 ng/mL with the minimum limit of detection of 2.0 fg/mL. The proposed platform was successfully applied to detect RBD in nasopharyngeal swab samples with satisfactory results. Furthermore, the paper-based immunosensor was extended to quantify the RBD level in spiked saliva samples, demonstrating the broadly applicability of this system. This electrochemical paper-based immunosensor has the potential to be employed as a point-of-care testing for COVID-19 diagnosis.

目前检测 SARS-CoV-2 感染的诊断平台的方法主要依赖于对现有技术的改造。在这项工作中，建立了一个简单且低成本的用于检测SAR-CoV-2抗原的电化学传感平台。所提出的传感器结合了创新的一次性纸基免疫传感器和具有成本效益的植物基抗 SARS-CoV-2 单克隆抗体 CR3022（在本塞姆氏烟草中表达）。在丝网印刷石墨烯电极上对纤维素纳米晶进行修饰，在电极表面提供丰富的COOH官能团，从而具有高的抗体固定能力。通过监测 [Fe(CN) ₆ ] ^3-/4-氧化还原溶液的电流变化，使用微分脉冲伏安法对 SARS-CoV-2 的存在受体结合域 (RBD) 刺突蛋白进行定量。可以清楚地区分目标 RBD 存在前后 [Fe(CN) ₆ ] ^3-/4-的电流变化，在 0.1 pg/mL 至 500 ng/mL 范围内与 RBD 浓度呈线性关系：最低检测限为 2.0 fg/mL。该平台成功应用于鼻咽拭子样本中的RBD检测，取得了满意的结果。此外，基于纸的免疫传感器被扩展用于量化加标唾液样本中的 RBD 水平，证明了该系统的广泛适用性。这种电化学纸质免疫传感器有潜力用作 COVID-19 诊断的即时检测。