The first real test for arsenic detection, The Marsh test, was discovered by James Marsh in 1836, and was used to reveal arsenic presence in case of arsenic poisoning in forensic science. It was the first method which could trace specifically the presence of arsenic in the body. It uses sulfuric acid and zinc. Here an arsenic crystal:
In 2009, At Jackson state university, the prof. Paresh Chandra Ray’s team developed a method using gold nanoparticles. Different organic molecules, which can grab arsenic ions, were attached on these nanoparticles. As up to three of these organic molecules can bind to one arsenic ion, the arsenic presence triggers formation of gold particles aggregate. As these particles turn from red color to blue color through these aggregation, the arsenic presence can be proved by colorimetry in a fast and simple way. It detects arsenic selectively and up to a concentration range of 1 ppb with naked eyes. But with a laser method called “dynamic light scattering”, the team was able to quantify the arsenic presence up to a concentration range of 3 ppt. The paper can be found here.
A similar approach was studied, at the beginning of 2013, by Indian scientists from Indian Association for the Cultivation of Science (IACS) which method uses gold clusters that emit light in presence of arsenic. This new technique is able to detect arsenic even in case of other metal ions presence. I think the technique is able to quantify the arsenic contamination level, because they say that the light emission grows proportionally to the arsenic contamination.
The iGEM Edinburgh’s team won the 2006 competition’s best poster and real world application prices, and they were the third on the best device podium. They genetically modified an E. Coli strain in order to rearrange the bacteria’s natural arsenic detection and detoxification system with the natural lactose degradation system so that the bacteria, when sensing arsenic in their environment, begin to break the lactose form the culture solution down and thus acidify it. The arsenic quantification is then identified with a simple pH test. They want to develop a “simple, cheap and sensitive field assay for arsenic levels” from the technology they found. Unfortunately, the method takes about five hours before given statisticaly valid results and it’s not sure that these test are valid for real water samples with a lot of other molecules and particles.
Another approach for arsenic detection is developped by the Oxford University’s business program Isis Innovation. They are thus unclear in the invloved method and only reveal that they use “modified glassy carbon electrodes electrochemical techniques. The advantage of this method seems to be that it detects low arsenic concentration even in copper (Cu(II)) presence which was a problem in the previous field test kits.
On the wagtech website, a specialist of water quality field test, There are at least two test for arsenic detection: The visual colour arsenic detection kit and the arsenator digital arsenic test. Both are low cost, portable, environnementaly friendly, and simple to use field kits. The first one works visualy, and compare the sample color after treatment to a list and detects until the range of 10 ppb. The second one gives valid results in 20 minutes, and detect in the range between 100 and 2 ppb.
A simple device which gives very rapid (15 to 120 second) and colour-based result is sold on the detectors for heavy metal website.
A paper written in 2005 by Dan Kroll, a scientist chief from the Hach company, a society which products medical and test measurement equipement in colorado, propose a method which is now largely used throughout the world because of it’s simplicity and safety. The protocol, as the Marsh test, uses hydrogen zinc and sulfide oxidized in sulfate, to reduce arsenite to arsine gas, which is then transformed into arsenic-mercuric halogenid with help of mercuric bromid. This halogenid colors the test paper and shows the arsenic presence, and the contamination level is probably quantified in comparing the color, which varies between white-yellow-tan-brown, with a comparison list. This test kit has the advantage that it substitutes liquid hydrochloric acid with a powder form, which decreases random effects, linked with the halogenid’s liquid form. Another advantage is the new design of the test tube which retains the arsine gas, a toxic compound, in order to force it to react entirely into the halogenid form. It increases the test’s sensitivity and avoids the arsin gas release wich problem was a real trouble of the other test kits.
Finally, a huge list of arsenic detection tools is available on the website contaminated site clean up information. It merit to be study.
So, this very little list of arsenic detection tools, which regroup only a small part of the large detection device variety, shows that equally the industry and the academical world are interested in this research field and that there are many different ways of detections. The goals are now to ensure that no more people continue to drink arsenic-contaminated water, and to stop industrial arsenic pollution.