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We report improvements on the heat transfer and on the control strategy of a thermal cycler implemented on a novel device for performing a fast polymerase chain reaction (PCR). The reduction of the thermal mass of the sample holder and the direct contact with the sample allow for a significant reduction of the transition times, while the hybrid feedforward/feedback controller can rely on inexpensive components (actuators, sensors, processor) and still achieve minimal over/undershooting and good temperature stability. The design of the device has been improved by performing transient heat conduction analysis on the highly heat-conductive sample holder and on the solid metal body of the device which rapidly dissipates the excess heat produced during the thermal cycling. In the current setup, the sample holder hosts nine 1 μL samples covered with mineral oil, which can be simultaneously read in real time by the detection module designed in-house and installed on the device. An increase in speed of the PCR amplification was achieved with a reduction of the transition time of 63.8% when compared against a commercial real-time PCR machine. Our work shows that a complete, stand-alone, and ready-to-use quantitative PCR instrument can be fabricated from inexpensive and easily available components and it can achieve fast thermal cycling thanks to a hybrid control strategy.

Farming, industry and urbanization lead to increases in the concentrations of potentially harmful compounds in waste, surface and drinking waters. One example of such pollution are estrogens, the steroidal female reproductive hormones. Already at a few nanograms per litre, these hormones can trigger endocrine disruption and cause acute and chronic health problems in humans and wildlife. Here, we present a Saccharomyces cerevisiae estrogen biosensor capable of detecting estradiol, as well as ethinylestradiol, at concentrations of 1 nM. After an initial characterization of the sensor strain performance in an optimal laboratory setting, we focused on developing a biosensor device. We addressed current limitations of biosensors, such as the requirement of the cells for a liquid growth matrix, controlled storage conditions required to preserve cell viability, and the usually required bulky, as well as expensive, laboratory equipment. Our study provides significant new insights into the field of applied biosensors. The system presented in this work takes microorganism-based analytics one step closer to field application in decentralized locations.