Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
ACS Nano. 2009 Dec 22;3(12):3869-77. doi: 10.1021/nn901025x.
We demonstrate the use of hydrogel swelling as a mechanism to reversibly induce solvatochromic shifting in single-walled carbon nanotube (SWNT) near-infrared emission within a biocompatible hydrogel. The optical sensor reports the degree of the swelled state and glucose concentration when apo-glucose oxidase is used to cross-link the hydrogel. Photoluminescence emission maxima from dispersed nanotubes in a poly(vinyl alcohol) hydrogel shift as cross-linking is increased, with a maximum of -48 meV for the (6,5) nanotube. The Raman tangential mode also red shifts up to 17 cm(-1), indicative of nanotube lattice strain equivalent to an effective hydrostatic pressure of 3 GPa. While the electronic band gaps of SWNTs are known to either increase or decrease with uniaxial strain or lattice deformation depending on chiral vector, we show that the mechanism of detection is counterintuitively non-strain-dependent. Instead, the data are well-described by a model that accounts for changes in dielectric screening of the 1-D exciton, as the osmotic pressure forces conformational distortions in the PVA by rotating more polar groups to the nanotube surface. The model describes observed changes with hydration state and cross-linking density variation from 0 to 14%. Cross-linking with apo-glucose oxidase renders the hydrogel glucose responsive, and we demonstrate rapid and reversible detection of glucose from these systems after repeated cycling of 10 mM glucose. We also demonstrate detection and imaging in the near-infrared of implanted hydrogel sensors in a mouse tissue model, showing excellent signal-to-noise of 8.6 and contrast with integration times of 60 s.
我们展示了水凝胶溶胀作为一种机制，可在生物相容性水凝胶内可逆地诱导单壁碳纳米管（SWNT）近红外发射的溶剂化变色。当使用去氧葡萄糖氧化酶交联水凝胶时，光学传感器报告溶胀状态的程度和葡萄糖浓度。分散在聚乙烯醇水凝胶中的纳米管的光致发光发射最大值随交联的增加而偏移，（6,5）纳米管的最大值为-48 meV。拉曼切线模式也红移了 17 cm(-1)，表明纳米管晶格应变等效于 3 GPa 的有效静水压力。虽然已知 SWNTs 的电子能带隙要么随着单轴应变或晶格变形而增加或减少，具体取决于手征向量，但我们表明，检测机制是反直觉的，与应变无关。相反，该数据由一个模型很好地描述，该模型考虑了 1-D 激子的介电屏蔽变化，因为渗透压通过将更多的极性基团旋转到纳米管表面来迫使 PVA 发生构象变形。该模型描述了观察到的与水合状态和交联密度从 0 到 14%变化的变化。用去氧葡萄糖氧化酶交联使水凝胶对葡萄糖具有响应性，并且我们在小鼠组织模型中展示了这些系统的快速和可逆检测，在 60 s 的积分时间内，信号与噪声比达到 8.6，对比度良好。
