Scientists turn cellphone into a chemical detector

Scientists have trained a cellphone camera to perform spectroscopy, turning the handheld device into a chemical detector, capable of identifying drugs, biological molecules and pathogens, according to a study published Tuesday in the Review of Scientific Instruments.

The device could be used for a variety of field applications, like surveying environmental contamination sites, screening for tainted food or diagnosing diseased crops, according to the researchers, from Texas A&M University.

"[The] outstanding quality and sensitivity of cameras in modern day cell-phones can ... be utilized as sensitive light detectors for various types of sensing," researchers wrote in the study.

"There have already been several successful attempts to utilize cell-phone cameras as portable digital light microscope systems," they wrote.

To turn the cellphone into a chemical detector, researchers developed a small diode laser that can be affixed to the phone's camera.

The accessory allows the cellphone to perform two kinds of spectroscopy, fluorescence spectroscopy and Raman spectroscopy.

Fluorescence spectroscopy measures the fluorescent light emitted by a sample, while Raman spectroscopy measures the vibrational frequency of target molecules.

Raman spectroscopy is useful for identifying biological molecules, including DNA and RNA, which are typically less fluorescent.

Spectroscopy involves the detection and measurement of different wavelengths.

Because different chemicals produce different spectral signatures, the digitized frequency spectrum captured by the cellphone camera can be used to identify the substances from which the light reflected off of or passed through.

The diode laser used by the research team at Texas A&M attaches to the cellphone camera at a right angle, preventing ambient and back-reflected light from entering the camera lens.

"In addition, this right-angle excitation geometry has the advantage of being easier to use for the analysis of samples where a bulk property is to be measured," lead author Peter Rentzepis said in a press release.

To test the new device, researchers aimed the camera-laser system at a range of liquid targets, including ethanol, acetone, isopropyl alcohol and methanol. Scientists also captured spectral signatures from solid objects, including a carrot and pellet of bacteria.

When researchers compared the spectral images captured by their cellphone system to the most sensitive commercial spectrometers, they found their images were about 10 times noisier.

However, researchers suggest the sensitivity of their cellphone spectrometer could be improved by utilizing High Dynamic Range applications, HDR, which combine multiple exposures to boost clarity and eliminate spectral noise.

For now, scientists said the inexpensive handheld chemical detector -- comparable commercial technologies cost at least a few thousand dollars -- works well enough to be deployed in the field.

"Our pocket sized designed and constructed Raman spectrometer system that utilizes right angle geometry to record Raman and resonance Raman spectra of molecules and biological species that contain colored pigments can be constructed for much lower cost," researchers wrote in the study.

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