Dipartimento di Ingegneria dell'Informazione, Università di Pisa , via G. Caruso 16, 56122 Pisa, Italy.
Anal Chem. 2016 Sep 6;88(17):8502-9. doi: 10.1021/acs.analchem.6b01228. Epub 2016 Aug 22.
Nanostructured porous silicon (PS) is a promising material for label-free optical detection of biomolecules, though it currently suffers of limited clinical diagnostic applications due to insufficient sensitivity. In this regard, here we introduce an ultrasensitive and robust signal processing strategy for PS biosensors that relies on the calculation of the average value over wavelength of spectral interferograms, namely IAW, obtained on PS interferometer by subtraction (wavelength by wavelength) of reflection spectra acquired after adsorption of biomolecules inside the nanopores from a reference reflection spectrum recorded in acetate buffer. As a case study, we choose to monitor bovine serum albumin (BSA) unspecific adsorption, which has been often employed in the literature as a model for proof-of-concept studies of perspective biosensing applications. The proposed IAW signal processing strategy enables reliable detection of BSA at concentrations in the range from 150 pM to 15 μM (down to 3 orders of magnitude lower than those targeted in the current literature) using a PS interferometer operating in label-free mode without any amplification strategies, with good sample-to-sample reproducibility over the whole range of tested concentrations (%CV = 16% over 5 replicates) and good signal-to-noise ratio also at the lowest tested concentration (S/N ≈ 4.6 at 150 pM). A detection limit (DL) of 20 pM (20 femtomoles, 1 mL) is estimated from the sigmoidal function best fitting (R(2) = 0.989) IAW experimental data over the whole range of tested concentrations. This is the lowest DL that has been reported in the literature since the seminal paper of Sailor and co-workers (1997) on the use of PS interferometer for biosensing, and lowers of 4 orders of magnitude DL attained with label-free PS interferometers using conventional effective optical thickness (EOT) calculation through reflective interferometric Fourier transform spectroscopy. Accordingly, the IAW signal processing strategy envisage bringing PS optical transduction at the forefront of ultrasensitive label-free biosensing techniques, especially for point-of-care clinical analysis where low analyte concentrations have to be detected in a small amount of biological samples.
纳米多孔硅（PS）是一种有前途的无标记光学生物分子检测材料，但由于灵敏度不足，目前其临床诊断应用有限。在这方面，我们为 PS 生物传感器引入了一种超灵敏和稳健的信号处理策略，该策略依赖于通过减去（逐波长）在纳米孔内吸附生物分子后获得的反射光谱与在醋酸缓冲液中记录的参考反射光谱来计算光谱干涉图的波长平均值，即 IAW。作为案例研究，我们选择监测牛血清白蛋白（BSA）的非特异性吸附，该吸附物在文献中常被用作有前途的生物传感应用概念验证研究的模型。所提出的 IAW 信号处理策略能够在无标记模式下使用 PS 干涉仪可靠地检测 BSA，浓度范围从 150 pM 到 15 μM（比当前文献中目标浓度低 3 个数量级），无需任何放大策略，在整个测试浓度范围内具有良好的样品间重现性（在 5 个重复中为 16%），并且在最低测试浓度下也具有良好的信噪比（在 150 pM 时约为 4.6）。从最佳拟合的（R(2) = 0.989）IAW 实验数据中，在整个测试浓度范围内估算出检测限（DL）为 20 pM（20 飞摩尔，1 毫升）。这是自 Sailor 及其同事（1997 年）在生物传感中使用 PS 干涉仪的开创性论文以来，文献中报道的最低检测限，与使用传统有效光学厚度（EOT）计算通过反射干涉傅里叶变换光谱的无标记 PS 干涉仪相比，DL 降低了 4 个数量级。因此，IAW 信号处理策略预计将使 PS 光学转换处于超灵敏无标记生物传感技术的前沿，特别是对于需要在少量生物样本中检测低浓度分析物的即时护理临床分析。
