In this communication, we demonstrate the electrical detection of SARS-CoV-2 RNA at low femtomolar concentrations without labels or amplification reactions. Following its extraction from virus particles, the viral RNA was electrokinetically preconcentrated (100-fold) within a packed bed of probe-modified microbeads. This preconcentration was accomplished by counter-flow focusing of the RNA along an electric field gradient generated by faradaic ion concentration polarization (fICP). Hybridization of the 30 kb target RNA to the probe-modified beads sufficiently altered their surface charge to yield a measurable change in the ionic conductivity of the packed bed─a feature leveraged for electrical detection. When a single-stranded DNA probe was used, the sensitivity of this enrichment and sensing scheme was low picomolar. However, the utilization of an uncharged PNA probe improved the limit of detection to 3.4 × 10⁶ viral copies/mL (22.5 fM SARS-CoV-2 RNA). These results are significant for three reasons. First, the sensitivity is remarkable, given the micrometer scale of both the beads and interstitial spaces. Additional gains in enrichment and sensitivity are anticipated as fundamental parametric studies and optimization are undertaken. Second, this study reveals the impact of the probe type on the sensitivity of microscale surface ion conduction (μSIC) sensors. Third, the RNA sensing approach has practical advantages including its utilization of off-the-shelf beads, a reagent-free approach, nonoptical readout, and low driving voltage, which render it amenable to point-of-care (POC) implementation.

中文翻译：

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在生物偶联微球填充床上对 SARS-CoV-2 RNA 进行电动预浓缩和无标记电检测


在本次通信中，我们展示了低飞摩尔浓度的 SARS-CoV-2 RNA 的电检测，无需标记或扩增反应。从病毒颗粒中提取后，病毒 RNA 在探针修饰的微珠填充床中进行电动预浓缩（100 倍）。这种预浓缩是通过沿法拉第离子浓度极化 （fICP） 产生的电场梯度对 RNA 进行逆流聚焦来实现的。30 kb 靶 RNA 与探针修饰的磁珠杂交充分改变了它们的表面电荷，从而在填充床的离子电导率中产生可测量的变化——这是用于电检测的特征。当使用单链 DNA 探针时，这种富集和感应方案的灵敏度为低皮摩尔。然而，使用不带电荷的 PNA 探针将检测限提高到 3.4 × 10⁶ 个病毒拷贝/mL（22.5 fM SARS-CoV-2 RNA）。这些结果很重要，原因有三。首先，考虑到珠子和间隙空间的微米尺度，灵敏度非常高。随着基础参数研究和优化的进行，预计富集和灵敏度会进一步提高。其次，本研究揭示了探针类型对微型表面离子传导 （μSIC） 传感器灵敏度的影响。第三，RNA 传感方法具有实际优势，包括利用现成的磁珠、无试剂方法、非光学读数和低驱动电压，使其适合床旁 （POC） 实施。