This paper reports a flexible precise volume sensor with metal-on-polyimide (PI) electrodes to substitute for the peripheral ration pump of a microfluidic system, thus beneficial for integration and miniaturization. This in-channel volume sensor consists of multi-electrode pairs, and it can perform volume measurement of the fluid flowing through microchannels by testing the resistance variation of the electrode pairs, which makes the device possible to help automatically control the sample volume in the mixing and reacting processes inside a microfluidic chip without peripheral ration pumps. The electrode pairs of the sensor are fabricated on flexible PI surface directly by inkjet printing. Then, the electrodes with the PI substrate are transferred and sandwiched by a polydimethylsiloxane (PDMS) substrate layer and a PDMS channel layer to form the flexible precise volume sensor. This method overcomes the challenge of patterning metals on PDMS and the sandwiched PDMS–PI–PDMS structure is beneficial for integration with other PDMS-based microfluidic chips. The effects of electrode-tip shapes and numbers of the electrode pairs are also investigated. A novel calculating method is proposed to obtain more precise results when different numbers of electrode pairs are used in different situations. According to the experimental results, the more electrode pairs are used in the same spacing, the better measurement precision can be obtained. The volume sensor with optimized electrode-tip and multi-electrode pairs can detect the fluid volume in nanolitre scales with the relative error of < 0.8%. This work exhibits the potential to form a total lab-on-a-chip without peripheral ration pumps.

本文报道了一种柔性的精密体积传感器，该电极带有聚酰亚胺金属（PI）电极，可替代微流体系统的外围定量泵，因此有利于集成化和小型化。该通道内体积传感器由多电极对组成，它可以通过测试电极对的电阻变化来执行对流经微通道的流体的体积测量，这使得该设备可以帮助自动控制混合过程中的样品体积无需外围定量泵即可在微流控芯片内部进行反应过程。传感器的电极对直接通过喷墨印刷在柔​​性PI表面上制造。然后，带有PI基板的电极被转移并被聚二甲基硅氧烷（PDMS）基板层和PDMS通道层夹在中间，以形成灵活的精密体积传感器。这种方法克服了在PDMS上对金属进行构图的挑战，并且将PDMS–PI–PDMS夹在中间的结构有利于与其他基于PDMS的微流控芯片集成。还研究了电极尖端形状和电极对数量的影响。提出了一种新颖的计算方法，以在不同情况下使用不同数量的电极对时获得更精确的结果。根据实验结果，在相同的间距下使用更多的电极对，可以获得更好的测量精度。具有优化的电极头和多电极对的体积传感器可以检测纳升级的流体体积，相对误差<0.8％。这项工作展示了无需外围定量泵即可形成整个芯片实验室的潜力。