Measuring absorption spectra of single molecules presents a fundamental challenge for standard transmission-based instruments because of the inherently low signal relative to the large background of the excitation source. Here we demonstrate a new approach for performing absorption spectroscopy in solution using a force measurement to read out optical excitation at the nanoscale. The photoinduced force between model chromophores and an optically trapped gold nanoshell has been measured in water at room temperature. This photoinduced force is characterized as a function of wavelength to yield the force spectrum, which is shown to be correlated to the absorption spectrum for four model systems. The instrument constructed for these measurements combines an optical tweezer with frequency domain absorption spectroscopy over the 400-800 nm range. These measurements provide proof-of-principle experiments for force-detected nanoscale spectroscopies that operate under ambient chemical conditions.

中文翻译：

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室温下使用光阱对力进行检测的纳米吸收光谱

测量单个分子的吸收光谱对于基于标准透射的仪器提出了一项基本挑战，因为相对于激发源的大背景而言，信号固有地较低。在这里，我们演示了一种新的方法，该方法在溶液中使用力测量来读取纳米级的光激发，从而在溶液中执行吸收光谱。在室温下，已在水中测量了模型生色团与光学捕获的金纳米壳之间的光诱导力。该光致作用力的特征在于波长的函数，以产生作用力光谱，该作用力光谱显示与四个模型系统的吸收光谱相关。用于这些测量的仪器将光学镊子与400-800 nm范围内的频域吸收光谱仪相结合。