#557 1956 · Alfred Free and Helen Murray Free (Miles Laboratories) · Medical diagnostics / chemistry
Testing urine for diabetes needed a test tube and a dropper, until someone asked why not just dip the paper in
the problem
Testing urine for diabetes required test tubes, droppers and washing between uses
background
Through the 1940s and early 1950s, testing a patient's urine for glucose meant a small wet-chemistry procedure: mix urine with reagent tablets in a test tube, watch for a color change. Miles Laboratories' own Clinitest tablets, introduced in 1941, were a real improvement on the older Benedict's reagent test (no Bunsen burner needed), but running the test still meant a test tube, a dropper to measure the urine sample, and washing the glassware afterward before the next patient — real friction for a test doctors wanted to run routinely.
Alfred and Helen Free, a husband-and-wife biochemist team at Miles's Ames Division, spent years making the tablet-and-tube test itself better: more sensitive, and, with a second reagent called Acetest, able to detect ketones as well as glucose. The improvements all stayed within the same basic apparatus — reagent in solid form, urine measured out with a dropper into a test tube, color read by eye. Nobody working on the problem had questioned whether the tube and dropper were actually necessary at all.
what everyone would do
Everyone improving urine testing, including the Frees themselves for years, worked within the same basic apparatus Clinitest had already established: reagent in a tablet, urine measured with a dropper into a test tube, color read by eye. The improvements that followed, better sensitivity, a second reagent for ketones, all made the reaction itself more accurate without questioning whether the tube, the dropper and the glassware washing were actually necessary at all.
what they saw
Al Free's question reframed the problem: the reagent didn't need to sit in a vessel waiting for urine to be measured into it, it could be carried on something a person dipped directly into the urine instead. Embedding the reagent chemistry onto a strip of filter paper eliminated the entire apparatus of measurement — no dropper needed a fixed quantity of liquid, because the strip itself only needed to be dipped and pulled back out to trigger the reaction.
the move
As Helen Free later recalled, Al Free asked a simple question: "we could get rid of the dropper if we just dipped the paper into the urine." Instead of measuring urine into a vessel holding the reagent, the team embedded the reagent chemistry directly onto a strip of filter paper — cut, dipped in reagent solution, and oven-dried — so a doctor or patient could simply dip the strip straight into a urine sample and read the resulting color change. The result, Clinistix, launched in 1956, used a two-stage enzyme reaction (glucose oxidase and peroxidase) that also made it specific to glucose, unlike Clinitest's tablets, which reacted to any sugar present.
why it works
Because the reagent lived on the strip rather than in a vessel waiting to be dosed, there was no longer a volume of urine to measure out precisely, no test tube to wash between patients, and no glassware to keep on hand at all — a doctor's office visit or eventually a patient's own bathroom could run the same test a hospital lab previously needed dedicated equipment for. Pairing that with a double enzyme reaction specific to glucose, rather than Clinitest's any-sugar reaction, meant the simplified format didn't come at the cost of accuracy, which is what let dip-and-read strips replace tube-based testing as the standard rather than remaining a lesser convenience option.
the payoff
Dip-and-read testing eliminated the test tube, the dropper, the glassware washing and the need for any measuring at all — a doctor, nurse or eventually a patient at home could get a reading from a single strip with no laboratory apparatus whatsoever. Miles extended the same dip-strip principle to protein (Albustix, 1957), then combined multiple reagents onto one strip (Uristix, 1957), eventually reaching a ten-test strip, Multistix 10 SG, by 1981.
where it breaks
This only works when the reaction itself can survive being dried onto a substrate and reactivated cleanly by a single dip, rather than needing precise volumes, timed mixing, or multiple sequential reagent additions that a static strip can't perform — the Frees' own path to Clinistix required real chemistry work to get a dried enzyme reaction to behave reliably and specifically. It also assumes a simple color-change readout is precise enough for the decision being made; tests that need quantitative precision beyond what a strip's color gradient can convey may still require the older, vessel-based approach or a dedicated reading instrument to interpret the strip.
what came after
Dip-and-read urine test strips became standard practice in physicians' offices, clinics and hospitals worldwide as a first-line screen for diabetes and kidney and liver disorders, and the same embed-the-reagent-on-a-strip principle underlies the at-home diabetes test strips still used today. The American Chemical Society designated the development of diagnostic test strips a National Historic Chemical Landmark in 2010.
references
- [1]Helen Free Advanced Diagnostic ChemistryNational Inventors Hall of Fame, 2023invent.org
- [2]Helen M. Free and Alfred FreeScience History Institute, 2021sciencehistory.org