Smart-phone, paper-based fluorescent sensor for ultra-low inorganic phosphate detection in environmental samples

• Published in: Microsystems & nanoengineering 2019-10, Vol.5 (1), p.1-10, Article 56
• Main Authors: Sarwar, Mehenur, Leichner, Jared, Naja, Ghinwa M., Li, Chen-Zhong
• Format: Article
• Language: English
• Subjects: 639/624; 639/624/1111; Algae; Engineering; Eutrophication; Fluorescence; Hypoxia; Optical communication; Response time; Smartphones
• ISSN: 2055-7434; 2096-1030; 2055-7434
• DOI: 10.1038/s41378-019-0096-8

A major goal of environmental agencies today is to conduct point-of-collection monitoring of excess inorganic phosphate (Pi) in environmental water samples for tracking aquatic “dead zones” caused by algae blooms. However, there are no existing commercial devices which have been miniaturized and are suitable for the point-of-need-testing (“PONT”) that is required to fully map a large region, such as the Florida Everglades. To solve this challenge, a reflection-mode fluorescence-sensing apparatus was developed, leveraging an environmentally sensitive fluorophore (MDCC) bound to a bacterial phosphate-binding protein to generate a fluorescent optical signal proportional to the concentration of (Pi) present. The combined end-to-end integrated sensor system had a response time of only 4 s, with minimal effects of common interfering agents and a linear range spanning from 1.1 to 64 ppb. To support ease-of-use during PONT, the platform incorporated disposable wax-printed paper strip sample pads and a smartphone camera detection system. Since the EPA threshold is currently 30 ppb to prevent eutrophication, this system serves as a rapid test of whether a region is compliant. A simple sensor for finding phosphates A disposable phosphate sensor that can be imaged directly with a smartphone could offer a simple and effective strategy for monitoring water contamination. The phosphates present in agricultural fertilizer can create an environmental disaster if they spill into surrounding water, producing algal ‘dead zones’. Standard methods for measuring inorganic phosphate are time-consuming and employ toxic chemicals, but researchers led by Chen-zhong Li at Florida International University (FIU) have developed a potential alternative for onsite testing. Teaming up with the Everglades Foundation, Li’s lab developed a paper-based sensor incorporating a fluorescently labeled bacterial protein, which generates a rapid visual readout upon binding to inorganic phosphate. Their sensor is capable of detecting whether phosphate levels in a water sample exceed legal limits and can be analyzed with a standard smartphone, making it a promising strategy for assessing contamination in the field.