Colorimetric Analysis Of Endotoxin Based On Gold Nanorods

Endotoxin(LPS), covering the outer membrane of the Gram-negative bacteria, can cause various effects on human, including fever, diarrhea, vomiting, septic shock and disseminated intravascular coagulation. Existence of large amount of endotoxin in food and injection products indicates bacterial contaminations and therefore poses threat to human health. The commom methods to detect endotoxin are time-consuming, with complex operations, and have a limited accuracy. On account of this, it is imperative to develop rapid and simple approaches for endotoxin detection. Recently, nanoscience has experienced rapid development. As a result, nanomaterials have been engaged in analytical science gradually, thus motivating food hazard detection and analysis. Gold nanorods(AuNRs), as special nanomaterials, are often used as sensor substrate for biomolecues analysis due to their unique physical and chemical properties. With adjustable LLSPR absorbance in visible region, AuNRs are widely used in colorimetric method.In this experiment, we report a method for rapid and visualized detection of endotoxin in food and injections taking advantage of the counterion electrostatic interaction between endotoxin and unmodified gold nanorods. We first fabricated 4 types of gold nanorods with different aspect ratio via seed-mediated and CTAB surfactant-directed method. Then 2 types were used to detect endotoxin. The positively charged gold nanorods can aggregate with negatively charged endotoxin through the counterion electrostatic attraction. Meanwile, we explored the performance of gold nanorods with different aspect ratios in color changes and sensitivity of quantitative determination. And the selectivity of this assay was also investigated. Finally, to validate the feasibility of the proposed method, three kinds of drink, and injection were chosen to test the accuracy of measurements.The results are as follow: First, Gold nanorods with aspect ratios from 2.3 to 3.8 were synthesized, and the corresponding colors are green, blue, red and brown. The peaks of longitudinal localized surface plasmon resonance appear at 635 nm, 690 nm, 750 nm and 795 nm respectively. Second, both the 2 types of Gold nanorods(green ones and red ones) are available to detect endotoxin sensitively, resulting in color changes and good linearship ranges. In this part, red nanorods(AR = 3.3) show advantages. The changes of UV-Vis spectra present a good linear relationship at 0.01-0.6 μM endotoxin with the detection limit to be 8.4 nM. With the addition of endotoxin, the color of gold nanorods suspension turned gray from red and eventually colorless. Third, the proposed assay presents satisfactory selectivity that not response to interferences. The recoveries range from 84% to 109% in spiked food and injection samples.The assay proposed in this paper is time-saving, easy-handled, cost-effective and visualized thus providing some fresh minds for the detecting of the endotoxin level in food and drugs and on-site screening of endotoxin in producing process. The method also provides a possibility for improving the current situation of food and drugs contamination by bacteria.