(179l) Sensing and Detection of Arsenic By Localized Surface Plasmon Resonance of Gold-Vitamin B12 Complex and a Device Thereof

Background: Arsenic contamination of water sources is a severe problem in various parts of the world. Drinking of arsenic containing water has serious consequences in terms of human health hazard and even death. In fact, because of its severe toxicity, the safe limit of arsenic in drinking water is only 10 ppb (parts per billion). In contrast, many contaminated sites have arsenic concentration upwards of that of hundreds of ppb. Thus, detection and measurement of arsenic concentration becomes a critical first step, in order to remove arsenic from water; so as to obtain safe, drinking water, which is fit for human consumption. In addition, because of the colourless, odourless and tasteless nature of arsenic present in water, it is a formidable challenge to have a handy and portable arsenic detection system, capable of measuring arsenic concentration fairly accurately and within minutes, down to the level of 10 ppb, or if possible, even for lower concentrations.

Principle: Our current research has resulted in the development of a sensor chemistry (between the gold-vitamin B12 complex developed by us and the arsenic contaminant), right up to the stage of a small device. In addition, we have achieved a high sensitivity and selectivity to arsenic concentration measurement, which can be detected from 100 ppb down to 10 ppb, quite accurately. This can be extended down to 0.1 ppb, based on the type of measurement device employed, using the same sensor chemistry and optical spectra based measurement-principle developed by us.

The detection and measurement is based on the reaction between - (i) a water-dispersible methylcobalamin (vitamin B12) containing gold nanoparticle solution, with (ii) a sample of arsenic containing water. Simple mixing of this in a cuvette results in a controlled aggregation of tiny gold nanoparticles of about 6-7 nm diameter, as arsenic binds to gold via our methylcobalamin sensor molecule. This translates into a shift in the local surface plasmon resonance of gold nanoparticle and gives an increase in its absorbance peak intensity, in the visible light range. This absorbance intensity is found to be very specific and selective to only arsenic and is proportional to the arsenic concentration in the water sample, from about 0.1 ppb upwards, up to 100 ppb.

Salient features of sensor: This effect and the mechanism behind it has been utilized by us to first have an on-board spectrometer system, and then further improve it to a small device (comprising of a LED light source and a photodiode), to help measure arsenic concentration very fast within minutes. This is in contrast to any unwanted delay (of 20-30 minutes) or use of other toxic chemicals, like mercury etc., which impedes other current testing kits.

Application: The sensor system can be used as a portable device to identify arsenic contamination and its value for different water-sources and water-bodies, very quickly. This is based on validation of results from our sensor-system with that of inductively coupled plasma mass spectrometric (ICP-MS) measurement of other synthetic and real-life environmental water samples.