Editorial Cite This: ACS Sens. 2018, 3, 239−239
pubs.acs.org/acssensors
Benchmarks and Breakthroughs
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fall somewhere in betweencontributing to the knowledge base that moves our entire field forward. But I think there is a discriminator. Often the key advance of a new discovery is not well suited to the application envisioned by the inventor, but it enables another application, whose critical need has not yet been identified. Thus, “just another” blood pH analyzer becomes a revolutionary high-throughput genome-sequencing tool. But in either case, the discovery is novel. The sensors in Walt’s randomized bead arrays were not newthey were based on well-established colorimetric or fluorescent reporters. But the means of placing them at the distal end of an optical fiber represented new knowledgea new material, a new process, and a revolutionary way of approaching a problem that discriminated this work from its competitors. Benchmarks are important because they give us a scoring system to determine how relevant a new sensor is for a particular application. But it is important that we not become so focused on today’s benchmarks that we miss tomorrow’s breakthroughs.
any years ago I was relaxing with Dick Crooks at the end of a long day of talks at a biosensors meeting. At that time we were both early career assistant professors, and the talk drifted to critiques of the sessions, the speakers, and the science presented that day. “One day I am going to organize a whole meeting on pH sensors,” Dick joked. “Everyone has to come talk about their latest, greatest sensor that does nothing but measure pH.” I should point out that Dick and I are not so old that we pre-date the pH meter. When we were assistant professors the pH meter was already a well-established, robust technology that was in no need of updating. My friend’s quip was poking fun at the fact that, at that time, it was common to demonstrate sensitivity by showing responses to proton activity as a surrogate for more interesting biological or biochemical analytes. The rationale was that the response to proton activity demonstrated the sensitivity of the technology, providing a benchmark that could be readily compared across devices. This practice is still common today, but as the field has matured it has become increasingly necessary to provide more relevant benchmarks: mass of analyte detected per area, wavelength shift per refractive index unit, etc. Sensitivity is one of several benchmarks we now look for at ACS Sensors (see Shana Kelley’s 2016 Editorial “Biomolecular Sensors: Benchmarking Basics” DOI: 10.1021/ acssensors.6b00775 for a more complete discussion). Then, as today, quantification of pH response provided limited benchmarking information in terms of how the sensor element might perform when challenged with various biological species of interest. But you have to crawl before you can walk. Although many of those early “pH sensors” never made the leap to more sophisticated applications, some of them did. One that did was the optical fiber-based sensors of David Walt,1 who showed that an imaging fiber could be used to probe multiple sensor elements simultaneously. His first application focused on real-time blood analysis of pH, with three discrete sensor elements at the distal end of the fiber. It was based on simple pH sensing molecules, but the implementation in an optical fiber was revolutionary. Before long, they had developed a means to etch micron-scale wells into the imaging fiber, and the device was massively expanded to thousands of elements containing a microscopic sensor bead in each well. Translation of this approach to nucleic acid analytes became the foundational DNA microarray technology for Illumina, Inc. At a present market capitalization of $32 billion, Illumina is one of the most successful biotechnology companies of all time. Within 15 years, Walt had reduced the size of the wells to the nanoscale, with sensitivities at the single molecule limit. This formed the core technology for a second company, Quanterix, whose technology focuses on detection of human biomarkers. Dick Crooks is now a chaired professor at the University of Texas at Austin, and he tells me he never did run his meeting on pH sensors. If Dick had indeed held this event, it would have been a challenge to discern which pH sensor would become a billion-dollar technology and which was destined to be buried in the scientific literature. The vast majority would © 2018 American Chemical Society
Michael J. Sailor, Associate Editor
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University of California, San Diego, California United States
AUTHOR INFORMATION
ORCID
Michael J. Sailor: 0000-0002-4809-9826 Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
(1) Barnard, S. M.; Walt, D. R. A fiber-optic chemical sensor with discrete sensing sites. Nature 1991, 353, 338.
EDITOR'S NOTE The author served as a technical consultant to Illumina from 1999 to 2003 and holds an equity interest in the company.
Received: February 5, 2018 Published: February 23, 2018 239
DOI: 10.1021/acssensors.8b00114 ACS Sens. 2018, 3, 239−239
