Muri Harald Ian, Bano Andon, Hjelme Dag Roar
Department of Electronic Systems, Norwegian University of Science and Technology, Gunnerus Gate 1, 7012 Trondheim, Norway.
Sensors (Basel). 2018 Jan 11;18(1):187. doi: 10.3390/s18010187.
We report on characterization of an optical fiber-based multi-parameter sensor concept combining localized surface plasmon resonance (LSPR) signal and interferometric sensing using a double-clad optical fiber. The sensor consists of a micro-Fabry-Perot in the form of a hemispherical stimuli-responsive hydrogel with immobilized gold nanorods on the facet of a cleaved double-clad optical fiber. The swelling degree of the hydrogel is measured interferometrically using the single-mode inner core, while the LSPR signal is measured using the multi-mode inner cladding. The quality of the interferometric signal is comparable to previous work on hydrogel micro-Fabry-Perot sensors despite having gold nanorods immobilized in the hydrogel. We characterize the effect of hydrogel swelling and variation of bulk solution refractive index on the LSPR peak wavelength. The results show that pH-induced hydrogel swelling causes only weak redshifts of the longitudinal LSPR mode, while increased bulk refractive index using glycerol and sucrose causes large blueshifts. The redshifts are likely due to reduced plasmon coupling of the side-by-side configuration as the interparticle distance increases with increasing swelling. The blueshifts with increasing bulk refractive index are likely due to alteration of the surface electronic structure of the gold nanorods donated by the anionic polymer network and glycerol or sucrose solutions. The recombination of biotin-streptavidin on gold nanorods in hydrogel showed a 7.6 nm redshift of the longitudinal LSPR. The LSPR response of biotin-streptavidin recombination is due to the change in local refractive index (RI), which is possible to discriminate from the LSPR response due to changes in bulk RI. In spite of the large LSPR shifts due to bulk refractive index, we show, using biotin-functionalized gold nanorods binding to streptavidin, that LSPR signal from gold nanorods embedded in the anionic hydrogel can be used for label-free biosensing. These results demonstrate the utility of immobilizing gold nanorods in a hydrogel on a double-clad optical fiber-end facet to obtain multi-parameter sensing.
我们报道了一种基于光纤的多参数传感器概念的特性，该概念结合了局域表面等离子体共振（LSPR）信号和使用双包层光纤的干涉传感。该传感器由一个微法布里-珀罗结构组成，其形式为半球形刺激响应水凝胶，在劈开的双包层光纤端面上固定有金纳米棒。水凝胶的溶胀程度通过单模内芯进行干涉测量，而LSPR信号则通过多模内包层进行测量。尽管水凝胶中固定有金纳米棒，但干涉信号的质量与先前关于水凝胶微法布里-珀罗传感器的工作相当。我们表征了水凝胶溶胀和本体溶液折射率变化对LSPR峰值波长的影响。结果表明，pH诱导的水凝胶溶胀仅导致纵向LSPR模式的微弱红移，而使用甘油和蔗糖增加本体折射率会导致大幅蓝移。红移可能是由于随着溶胀增加粒子间距离，并排配置的等离子体耦合减少所致。随着本体折射率增加的蓝移可能是由于阴离子聚合物网络以及甘油或蔗糖溶液对金纳米棒表面电子结构的改变。水凝胶中金纳米棒上生物素-链霉亲和素的重组显示纵向LSPR出现7.6 nm的红移。生物素-链霉亲和素重组的LSPR响应是由于局部折射率（RI）的变化，这有可能与由于本体RI变化引起的LSPR响应区分开来。尽管由于本体折射率导致LSPR有较大位移，但我们通过生物素功能化金纳米棒与链霉亲和素结合表明，嵌入阴离子水凝胶中的金纳米棒的LSPR信号可用于无标记生物传感。这些结果证明了将金纳米棒固定在双包层光纤端面的水凝胶中以实现多参数传感的实用性。
