High-frequency phase shift measurement greatly enhances the sensitivity of QCM immunosensors

• By means of a new electronic characterization approach, we have developed an HFF-QCM versatile immunosensor.
• This approach is based on phase shift measurements.
• The HFF-QCM immunosensor has been tested for its use in sensitive pesticide determinations.
• Analytical performance obtained with 100 MHz QCM sensors, widely improves that of conventional QCM and SPR immunosensors and approaches the most sensitive ELISA.

In spite of being widely used for in liquid biosensing applications, sensitivity improvement of conventional (5–20 MHz) quartz crystal microbalance (QCM) sensors remains an unsolved challenging task. With the help of a new electronic characterization approach based on phase change measurements at a constant fixed frequency, a highly sensitive and versatile high fundamental frequency (HFF) QCM immunosensor has successfully been developed and tested for its use in pesticide (carbaryl and thiabendazole) analysis. The analytical performance of several immunosensors was compared in competitive immunoassays taking carbaryl insecticide as the model analyte. The highest sensitivity was exhibited by the 100 MHz HFF-QCM carbaryl immunosensor. When results were compared with those reported for 9 MHz QCM, analytical parameters clearly showed an improvement of one order of magnitude for sensitivity (estimated as the I50 value) and two orders of magnitude for the limit of detection (LOD): 30 μg l−1 vs 0.66 μg L−1I50 value and 11 μg L−1 vs 0.14 μg L−1 LOD, for 9 and 100 MHz, respectively. For the fungicide thiabendazole, I50 value was roughly the same as that previously reported for SPR under the same biochemical conditions, whereas LOD improved by a factor of 2. The analytical performance achieved by high frequency QCM immunosensors surpassed those of conventional QCM and SPR, closely approaching the most sensitive ELISAs. The developed 100 MHz QCM immunosensor strongly improves sensitivity in biosensing, and therefore can be considered as a very promising new analytical tool for in liquid applications where highly sensitive detection is required.