Detection and Spatial Mapping of Mercury Contamination in Water Samples Using a Smart-Phone

Abstract

Detection of environmental contamination such as trace-level toxic heavy metal ions mostly relies on bulky and costly analytical instruments. However, a considerable global need exists for portable, rapid, specific, sensitive, and cost-effective detection techniques that can be used in resource-limited and field settings. Here we introduce a smart-phone-based hand-held platform that allows the quantification of mercury(II) ions in water samples with parts per billion (ppb) level of sensitivity. For this task, we created an integrated opto-mechanical attachment to the built-in camera module of a smart-phone to digitally quantify mercury concentration using a plasmonic gold nanoparticle (Au NP) and aptamer based colorimetric transmission assay that is implemented in disposable test tubes. With this smart-phone attachment that weighs <40 g, we quantified mercury(II) ion concentration in water samples by using a two-color ratiometric method employing light-emitting diodes (LEDs) at 523 and 625 nm, where a custom-developed smart application was utilized to process each acquired transmission image on the same phone to achieve a limit of detection of ∼3.5 ppb. Using this smart-phone-based detection platform, we generated a mercury contamination map by measuring water samples at over 50 locations in California (USA), taken from city tap water sources, rivers, lakes, and beaches. With its cost-effective design, field-portability, and wireless data connectivity, this sensitive and specific heavy metal detection platform running on cellphones could be rather useful for distributed sensing, tracking, and sharing of water contamination information as a function of both space and time.

Broadly Available Imaging Devices Enable High-Quality Low-Cost Photometry

“…[20][21][22][23][24][25][26][27][28][29] For example, we and others have constructed low-cost photometers based on this principle to measure i) antibodies against HIV in serum, 21 ii) hemoglobin [22][23] in blood, and iii) fluoride 27 and mercury 29 in water samples.…”

O-Phenylenediamine-Cysteine Nanosphere Having Conjugated Structures: A Highly Selective Fluorescent Probe for Mercury Ion

“…Therefore, it is especially important for studying new method with high sensitivity and selectivity to detect the trace amounts of Hg 2+ in water [8,9]. Various methods for detecting Hg 2+ from nature water and industrial waste have been extensively used, including photoelectrochemical method, atomic absorption spectroscopy (AAS), coupled plasma mass spectrometry (ICP-MS), surface enhanced Raman scattering (SERS), fluorescence spectrophotometer, electro-deposition [12][13][14]. Among these, fluorescence spectrophotometer is one of the most attractive methods because of its simplicity, low-cost and ectiveness for water treatment.…”

Early warning smartphone diagnostics for water security and analysis using real-time pH mapping

“…Such a smartphone technology is increasingly reported recently as a field-portable platform for many applications specially in bio-diagnostic and environmental monitoring. Most of these approaches are based on simple colorimetry [8][9][10][11][12][13][14][15][16], imaging [17][18][19][20][21][22][23], and spectroscopy [24][25][26][27]. Paper microfluidic devices are sometimes integrated to the calorimetric approaches [28][29][30][31][32][33][34][35].…”

“…This makes them ideal for use in networked systems. Mapping of heavy metal ion detection using two parts colorimetric analysis has been reported using a smartphone [9], but this approach involves integration of two external diode sources and power supplies to image the samples, which greatly limits device accessibility for a large part of the world.…”