Luminescence lifetime-based sensing: new materials, new devices

Advantages of luminescence-lifetime over intensity measurements in sensing applications include independence of variations in source intensity, detector sensitivity, light throughput and, most importantly, indicator concentration. Nevertheless, most researchers still believe that lifetime measurement needs highly sophisticated instrumentation and hence is unsuitable for practical applications. In this contribution it will be shown that this is no longer true. With the advent of more powerful blue light-emitting diodes, virtually the whole visible part of the spectrum can be covered by low-cost light sources. Typical singlet excited-state lifetimes are in the range of some nanoseconds. Recently, however, luminophores with lifetimes from hundreds of nanoseconds up to hundreds of microseconds have been introduced to optical sensing. Families of sensor dyes, all members being based on the same 'long' luminophore but covering a number of different analytes, have been developed. Lifetime sensing is hence no longer restricted to ultrashort times. Standard electronics as used in consumer circuits can be applied in low-cost lifetime instrumentation, Thus a whole range of analytes, from oxygen, pH and CO, over cations and onions to glucose can be measured by cheap and reliable lifetime-based sensor devices.