In oligotrophic regions, ammonium (NH) concentrations can be below 50 nM, however, few existing instruments can measure below this level with high confidence. This work, based on the o-pthaldialdehyde (OPA) fluorescence assay, is applied to measure nanomolar NH in a novel optofluidic Cyclic Olefin Copolymer (COC) microchip using a low-power (20 mW) Light Emitting Diode (LED) as the excitation source. The optical arrangement was first modeled using ray tracing software to determine the initial detection volume size. Ammonium standards made with artificial seawater of 5 nM to 1000 nM, were run in triplicates. The limit of detection (LOD) obtained was 1.5 nM (3 x σ of the blank) or a LOD of 15 nM when the y-intercept and the vertical variation of each measured concentration on the calibration curve were taken into consideration (y-intercept +3. S ). Precision at 5 nM and 1000 nM was 3.3% and 0.5% respectively. The optofluidic system was also compared to an off-the-shelf fluorometer (Jasco FP2020) and an existing high-resolution shipboard analyser using five different standard concentrations. The LOD and the ammonium concentrations uncertainty for the Jasco FP2020, shipboard analyser, and current microsystem were 217 nM, 39 nM, and 15 nM and ± 232 nM, ± 48 nM, and ± 16 nM respectively. The optical setup was also validated using real samples from the Atlantic. This optical design, without optical fibres, makes the system simple and suitable for use with other fluorescent assays when compact, rugged, low-cost, and low-power consumption instrumentation is required.

中文翻译：

---

利用环烯烃共聚物微芯片和低功率 LED 测量纳摩尔铵

在营养贫乏地区，铵 (NH) 浓度可能低于 50 nM，但是，很少有现有仪器能够以高置信度测量低于此水平的数据。这项工作基于邻苯二醛 (OPA) 荧光测定，采用低功率 (20 mW) 发光二极管 (LED) 作为激发，在新型光流控环烯烃共聚物 (COC) 微芯片中测量纳摩尔 NH来源。首先使用光线追踪软件对光学装置进行建模，以确定初始检测体积大小。使用 5 nM 至 1000 nM 的人造海水制备的铵标准品一式三份。获得的检测限 (LOD) 为 1.5 nM（空白的 3 x σ）或当考虑 y 截距和校准曲线上每个测量浓度的垂直变化（y 截距）时，LOD 为 15 nM +3.S）。 5 nM 和 1000 nM 的精度分别为 3.3% 和 0.5%。该光流控系统还与现成的荧光计 (Jasco FP2020) 和使用五种不同标准浓度的现有高分辨率船载分析仪进行了比较。 Jasco FP2020、船载分析仪和电流微系统的 LOD 和铵浓度不确定度分别为 217 nM、39 nM 和 15 nM，以及 ± 232 nM、± 48 nM 和 ± 16 nM。光学设置还使用来自大西洋的真实样本进行了验证。这种无光纤的光学设计使系统变得简单，并且适合在需要紧凑、坚固、低成本和低功耗仪器时与其他荧光测定一起使用。