Scientists have found a way to find minute, previously undetected, traces of cocaine on surfaces, they said.
The research, carried out at the University of Derby using a new method of forensic analysis, may help police find tiny traces of the drug - and other drugs - on a range of surfaces.
Sonica Devi, 22, a final year student at the university, developed the novel technique to find traces of cocaine at various phone boxes in Derby.
A standard method would easily have missed the low levels she managed to find.
The university said she used an ultra sensitive Gas Chromatographic technique which allowed her to find cocaine at picogram levels - one million millionth of a gram - from forensic swabs.
Gas Chromatography linked to a mass spectrometer is an established technique for separating complex mixtures of compounds and detecting them down to very low amounts.
The new breakthrough makes detection of the drug possible even at a million millionth of a gram.
A picogram is one thousand times smaller than a nanogram and a thousand thousandth times smaller than a microgram (a millionth of a gram).
Ms Sonica's study, entitled Real world detection of cocaine at the picogram (one trillionth of a gram) level in an urban environment is now being presented at a number of forensic science conferences across the UK.
The 22-year-old, from Littleover, Derby, said: "I had no idea what I would find through this study as no trace of drugs could be seen in the phone booths with the naked eye - I was surprised at what the research found.
"I am keen to take this research forward and would be keen to work with other agencies or organisations to develop this further."
Using her new approach, Sonica was able to see even the smallest of traces of cocaine in samples collected around the city.
The lowest amount she could detect was 50 parts per million million - 50 picograms.
The study revealed that in one phone box cocaine was present at a higher level of 10 nanograms and in the other five boxes tested, it was detected at varying levels approaching the limit of detection - 50 picograms.
For the study, sterile swabs were used to collect samples from different areas of each box including dial, handset, key pad and coin slot.
Samples were taken using a variety of swabs: Wetted with ethanol; wetted with water and dry swabs to maximise how much cocaine could be lifted from the surfaces.
The swabs were taken back to the university's laboratories for analysis and each placed in tubes containing the solvent Dichloromethane (DCM), which dissolves the cocaine and allows it to enter the Gas Chromatograph.
After separating the cocaine from other materials the mass spectrometer detector gives a way of detecting the cocaine - using the method developed by Sonica this was performed with extremely high sensitivity.
Senior lecturer Alan-Shaun Wilkinson supervised Sonica during this project, helped by Joe Waldron - an expert in the use of GCMS at the university.
He said Ms Sonica embarked on the research after speaking to police.
"They were suggesting that that might be something worth investigating because of the association with drug dealers using phone boxes," he said.
"Although obviously mobile phones are used considerably these days, they had strong suspicions that these phone boxes would be used by certain people dealing drugs and that was borne in the study.
"You could equally apply the same technique to swabbing mobile phone handsets or any other surface to reveal tiny traces of drugs.