基于多正弦调制光镊的单脉冲宽带主动微流变学研究
Single-shot wideband active mircorheology using multiple-sinusoid modulated Optical Tweezers
摘要：
我们采用多个正弦调制光镊测量线性粘弹性流体的频率依赖的流变参数超过五十年的频率在一个Single Shot，迄今没有实现单独使用主动微流变学。因此，我们在空间上调制嵌入在流体介质中的捕获的探针粒子与方波的组合-这是由定义的奇正弦谐波的叠加-和多个正弦波在宽带频率范围内的线性叠加，与调制信号的振幅，频率和相对相位的完全控制。对于后者，我们选择性地激发粒子在高频率的粒子响应是低的较大幅度，从而使宽带主动微流变学与大的信号噪声。这减轻了与传统的主动微流变学相关的主要问题-这是低带宽-并且还使我们的方法在信噪比方面更好，并且与被动微流变学相比更快。我们确定复杂的粘弹性参数的流体提取的相位响应（相对于输入激励）的探头从实验记录的时间序列数据的探头位移，并采用众所周知的理论相关性。我们通过研究不同浓度的线性粘弹性介质（聚丙烯酰胺-水溶液）来测试我们的方法的有效性，并发现测量的流体参数与已知文献值的良好一致性。
英文摘要：
We employ multiple sinusoid modulated optical tweezers to measure the frequency dependent rheological parameters of a linear viscoelastic fluid over five decades of frequency in a single shot, hitherto not achieved using active microrheology alone. Thus, we spatially modulate a trapped probe particle embedded in a fluid medium with a combination of a square wave - which is by definition a superposition of odd sinusoidal harmonics - and a linear superposition of multiple sinusoids at a wideband frequency range, with complete control over the amplitude, frequency and relative phase of the modulating signals. For the latter, we selectively excite the particle by larger amplitudes at high frequencies where the particle response is low, thereby enabling wideband active microrheology with large signal-to-noise. This mitigates the principal issue associated with conventional active microrheology - which is low bandwidth - and also renders our method better in terms of signal to noise, and faster compared to passive microrheology. We determine the complex viscoelastic parameters of the fluid by extracting the phase response (relative to input excitation) of the probe from the experimentally recorded time series data of the probe displacement, and employing well-known theoretical correlations thereafter. We test the efficacy of our method by studying a linear viscoelastic media (polyacrylamide-water solution) at different concentrations, and find good agreement of the measured fluid parameters with known literature values.
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