The paper reports a simple enzyme-free colorimetric sensor for the detection of cardiac marker, Troponin I (cTnI) based on the self-assembly of gold nanorods (AuNRs) on heparin. The sensing system consists of a purple colour solution of Hexadecyltrimethylammonium bromide (CTAB) stabilised AuNRs self-assembled in presence of heparin due to the electrostatic interaction resulting in the reduction of surface plasmon absorption (SPR) of AuNRs and hence colour quenching/change of solution from red to blue. However, in the presence of cTnI, the electrostatic balance was disturbed due to the strong complex forming tendency between heparin and cTnI which was attributed due to the stronger complex forming tendency between the sulphate and carboxylate group of glycosaminoglycans and heparin binding proteins present in cTnI. Hence, the AuNRs are left free in the solution and retains the native red colour of the solution. As the concentration of cTnI in the solution was increased, the colour gradually changes from blue to red there by enabling the sensing of cTnI. The above mechanisms were confirmed by transmission electron microscopy. The AuNR aggregation was found to be inversely proportional to the concentration of cTnI. The change in absorbance of AuNRs with different concentrations of cTnI was monitored by UV-Visible spectroscopy. Using this sensor system, cTnI in the range of 0.5–15 ng/mL could be measured with a detection limit of 0.4 ng/mL. The system also showed good selectivity in presence of different competing substances under the same experimental conditions. The method appears to be simple, cost effective, and would be highly be beneficial in rural health care centres where high tech diagnostic aids are inaccessible.

中文翻译：

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基于金纳米棒在肝素上自组装的心肌肌钙蛋白 I (cTnI) 非酶比色传感器

该论文报告了一种简单的无酶比色传感器，用于检测心脏标志物肌钙蛋白 I (cTnI)，该传感器基于肝素上金纳米棒 (AuNR) 的自组装。传感系统由十六烷基三甲基溴化铵 (CTAB) 稳定的 AuNR 的紫色溶液组成，在肝素存在下自组装，由于静电相互作用导致 AuNR 的表面等离子体吸收 (SPR) 减少，因此溶液的颜色淬灭/变化从红色到蓝色。然而，在 cTnI 存在的情况下，由于肝素和 cTnI 之间的强复合物形成趋势，静电平衡被扰乱，这是由于 cTnI 中存在的糖胺聚糖的硫酸盐和羧基与肝素结合蛋白之间更强的复合物形成趋势。因此，AuNRs 留在溶液中并保留溶液的天然红色。随着溶液中 cTnI 浓度的增加，通过启用 cTnI 的感应，颜色逐渐从蓝色变为红色。上述机制已通过透射电子显微镜证实。发现 AuNR 聚集与 cTnI 的浓度成反比。通过紫外-可见光谱监测具有不同浓度 cTnI 的 AuNRs 吸光度的变化。使用该传感器系统，可以测量 0.5–15 ng/mL 范围内的 cTnI，检测限为 0.4 ng/mL。在相同的实验条件下，该系统在不同竞争物质的存在下也表现出良好的选择性。该方法看似简单，性价比高，