Micro-pHAT: A re-envisioned sensor design for measuring seawater pH and Total Alkalinity in situ

海洋在全球碳循环中发挥着不可或缺的作用，向大气排放的二氧化碳增加导致海洋变暖和海洋酸化，对海洋生态系统产生连锁效应。基于海洋的二氧化碳清除战略正在获得大量关注，需要监测、报告和核查以及评估潜在的环境影响。传统上，船基平台被用来收集海水样本进行台式分析，这产生了海洋碳化学的高质量快照。然而，船基平台在其时空分辨率方面是有限的，这导致了各种自主平台的发展，以填补空间和时间上的空白。到目前为止，还没有商业上可获得的用于测量适合于原位自主平台的全海水二氧化碳系统的单个传感器。该项目将重点提高用于测量pH值和总碱度的原型传感器（Sea-pHAT）的技术成熟度水平。这种双参数传感器不需要外部试剂，功耗低，速度快（每次测量约60秒），占地面积小，并且是固态的，所有这些都使其适用于原位自主平台。这种传感器是独一无二的，因为大多数其他正在开发的测量海水二氧化碳系统的技术需要试剂，具有复杂的移动部件，并且不能几乎同时测量两个参数。Sea-pHAT是一种基于ISFET（离子敏感场效应晶体管）的pH传感器，通过添加库仑致动器设备进行了修改，以在芯片上额外执行碱度滴定。在其当前配置中，致动器电极（阳极）直接沉积在ISFET芯片的表面上。我们将设计一个微流体型外壳，它将替代地将阳极悬挂在芯片（门）的离子感测区域上方，并具有可调节的垂直定位。这具有若干益处，包括阳极栅极的动态调整。阳极-栅极距离的严格表征将与Sea-pHAT传感器的可调Micro-pHAT和改进的ISFET并排进行。最佳阳极-栅极距离将在不同的AT范围内确定，并将评估测量对温度和盐度的灵敏度。将探索信号调节例程以优化传感器输出，并将其集成到传感器软件中。所有测试配置的结果将综合在用户手册中，以帮助未来用户选择最佳操作参数和了解系统选项。所有这些都将使我们更接近于拥有一种商业化的、用户友好的、单浸式探头，用于测量整个二氧化碳水溶液系统，可以集成在各种平台上。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The oceans play an integral role in the global carbon cycle and increased carbon dioxide emissions to the atmosphere have resulted in ocean warming and ocean acidification with cascading effects on marine ecosystems. Ocean-based carbon dioxide removal strategies are gaining a lot of attention and will require monitoring, reporting, and verification as well as evaluation of potential environmental impact. Traditionally, ship-based platforms have been used to collect seawater samples for benchtop analyses which has generated high quality snapshots of the ocean carbon chemistry. However, ship-based platforms are limited in their spatiotemporal resolution which has led to the development of a variety of autonomous platforms for filling in the gaps in both space and time. To date, there is no commercially available, single sensor for measuring the full seawater carbon dioxide system suitable for in situ, autonomous platforms. This project will focus on advancing the technology readiness level of a prototype sensor (Sea-pHAT) for measuring both pH and Total Alkalinity. This two-parameter sensor does not require external reagents, is low power, is fast (about 60 seconds per measurement), has a small footprint, and is solid-state all of which lend it to be suitable and ideal for in situ, autonomous platforms. This sensor is unique because most other developing technologies for measuring the seawater carbon dioxide system require reagents, have complex moving parts, and cannot measure two parameters near simultaneously. The Sea-pHAT is an ISFET-based (ion sensitive field effect transistor) pH sensor that has been modified through the addition of a coulometric actuator device to additionally perform an alkalinity titration on the chip. In its current configuration, the actuator electrode (anode) is deposited directly on the surface of the ISFET chip. We will design a microfluidic-type housing that will instead suspend the anode above the ion sensing region of the chip (gate) with adjustable vertical positioning. This has several benefits including on the fly adjustment of the anode-gate. A rigorous characterization of the anode-gate distance will be performed side-by-side with the tunable Micro-pHAT and modified ISFETs of the Sea-pHAT sensor. The optimal anode-gate distance will be determined over various ranges of AT and sensitivity of the measurement to temperature and salinity will be assessed. Signal conditioning routines will be explored to optimize the sensor output and will be integrated in the sensor software. The results from all the configurations tested will be synthesized in a user manual to aid future users in selecting optimal operating parameters and understanding system options. All of this will result in bringing us several steps closer to having a commercially available, user friendly, single dip probe for measuring the full aqueous carbon dioxide system that can be integrated on a variety of platforms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.