The optimal frequency (OF) of a biomarker in electrochemical impedance spectroscopy (EIS) is the frequency at which the EIS response best reflects the binding of the biomarker to its molecular recognition element. Commonly, biosensors rely on complicated immobilization chemistry to attach biological molecules to the sensor surface, making the direct study of a biomarker’s native OF a challenge. Physical adsorption presents a simple immobilization strategy to study the native biomarker’s OF, but its utility is often discouraged due to a loss in biological activity. To directly study a biomarker’s native OF and investigate the potential of OF to overcome the limitations of physical adsorption, a combination of EIS and glutaraldehyde-mediated physical adsorption was explored. The experimental sensing platform was prepared by immobilizing either anti-lactoferrin (Lfn) IgG or anti-immunoglobulin E (IgE) onto screen printed carbon electrodes. After characterizing the native OFs of both biomarkers, investigation of the platform’s specificity, stability, and performance in complex medium was found to be sufficient. Finally, a paper-based tear sampling component was integrated to transform the testing platform into a prototypical point-of-care dry eye diagnostic. The investigation of native OFs revealed a correlation between the native OFs (57.44 and 371.1 Hz for Lfn and IgE, respectively) and the molecular weight of the antibody–antigen complex. Impedance responses at the native OFs have enabled detection limits of 0.05 mg/mL and 40 ng/mL for Lfn and IgE, respectively, covering the clinically relevant ranges. The native OFs were found to be robust across various testing mediums and conditions.

中文翻译：

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通过基于物理吸附的固定化直接测量生物标志物的固有最佳频率

电化学阻抗谱（EIS）中生物标记的最佳频率（OF）是EIS响应最能反映生物标记与其分子识别元件的结合的频率。通常，生物传感器依靠复杂的固定化化学方法将生物分子附着到传感器表面，这使得直接研究生物标志物的天然OF成为一个挑战。物理吸附为研究天然生物标志物的OF提供了一种简单的固定策略，但由于生物活性的丧失，通常不鼓励使用它。为了直接研究生物标志物的天然OF并研究OF克服物理吸附限制的潜力，探索了EIS和戊二醛介导的物理吸附的组合。通过将抗乳铁蛋白（Lfn）IgG或抗免疫球蛋白E（IgE）固定在丝网印刷的碳电极上，可以制备实验感测平台。在对两种生物标志物的天然OF进行表征后，发现对该平台的特异性，稳定性和在复杂培养基中的性能进行研究就足够了。最后，集成了一个基于纸张的泪液采样组件，以将测试平台转变为原型的即时医疗点干眼诊断。对天然OFs的研究揭示了天然OFs（Lfn和IgE分别为57.44和371.1 Hz）与抗体-抗原复合物的分子量之间的相关性。天然OF处的阻抗响应使Lfn和IgE的检出限分别为0.05 mg / mL和40 ng / mL，涵盖了临床相关范围。