Biophotonic Ring Resonator for Ultrasensitive Detection of DMMP As a Simulant for Organophosphorus Agents Karine Bonnot,* ,† Francisco Cuesta-Soto, ‡ Manuel Rodrigo, ‡ Antonio Varriale, § Nuria Sanchez, ⊥ Sabato D’Auria, § Denis Spitzer, † and Francisco Lopez-Royo ⊥ † Nanomate ́ riaux pour les Systè mes Sous Sollicitations Extrê mes (NS3E), French-German Research Institute of Saint-Louis, UMR 3208 CNRS/ISL/UDS, 68301 Saint-Louis, France ‡ DAS Photonics, Ciudad Polite ́ cnica de la Innovació n, 46022 Valencia, Spain § Istituto di Biochimica delle Proteine, Consiglio Nazionale delle Ricerche, 80131 Napoli, Italy ⊥ Nanophotonics Technology Center, Universitat Polite ̀ cnica de Valè ncia, 46022 Valencia, Spain ABSTRACT: Combining photonic integrated circuits with a biologically based sensing approach has the ability to provide a new generation of portable and low-cost sensor devices with a high specificity and sensitivity for a number of applications in environmental monitoring, defense, and homeland security. We report herein on the specific biosensing under continuous air flow of DMMP, which is commonly used as a simulant and a precursor for the synthesis of Sarin. The proposed technology is based on the selective recognition of the targeted DMMP molecule by specifically modified proteins immobilized on photonic structures. The response of the biophotonic structures shows a high stability and accuracy over 3 months, allowing for the detection in diluted air of DMMP at concentration as low as 35 μg/m 3 (6.8 ppb) in less than 15 min. The performance of the developed technology satisfies most current homeland and military security requirements. B ecause of their versatility, optical sensors are powerful detection and analysis tools with many applications: environmental and industrial monitoring, defense and border security, and for the surveillance of large areas such as airports and stadiums. 1 Under this category, there exist various optical detection methods, including refractive index change, optical absorption, and infrared or Raman spectroscopy. 2,3 We chose to focus on the approach of the photonic measurement of changes in the refractive index (RI) of a sensitive surface derivatized with a biomolecule able to bind to a specific targeted analyte. Refractive index is widely used for the monitoring of chemical processes and implementation in photonic integrated circuits (PIC), and it holds great promise for the development of mobile, low-cost sensor arrays for real time monitoring. 4 For use in such integrated systems, many resonating techniques can be employed, such as surface plasmon resonance, 5 Mach-Zehnder interferometer, 6 and optical waveguide and ring resonator-based biosensors. 7-9 To allow selective detection of small molecules at very low concentrations (parts per billion, parts per trillion, and even parts per quadrillion), molecular recognition approaches show great potential in the capture of molecules. This approach is frequently combined with labeling molecules or fluorescent tags. 10,11 A label-free approach such as the one presented in this work yields some benefits. The detection procedure is easier and less expensive to perform and permits quantitative and kinetic measurements of molecular interaction between a sensitive layer and the targeted analyte. 12,13 The work presented herein exploits the capability of monitoring interactions between targeted molecules and a specific layer of proteins immobilized on a ring resonator-based chip. The high selectivity of biosensors compared with chemical sensors lies in the use of very speci fically occurring biomolecules, such as enzymes, antibodies, etc. The concept of molecular recognition of a bioreceptor to a targeted analyte mimics the immunological response of some animals. In analogy with dogs’ detection of drugs and illicit substances, the proposed technology is based on the combination of bioreceptors with a photonic detection of binding molecules. Specific detection needs for defense against chemical and biological threats could be addressed with PIC biosensor-based devices for monitoring and detecting the release of toxic substances, such as nerve agents, in air in large areas. As an example, because of its high toxicity and the fact that noticeable health effects have been observed for an exposure of 30 min at concentration levels of 8.5 ppb, devices achieving a fast detection of Sarin at the parts-per-billion level within minutes are mandatory. 14 DMMP is a precursor of Sarin (GB) nerve gas, and it is actually used as a simulant for many organophosphorus toxic compounds. Because of its low stability in air, it is often detected in aqueous media. 15 In the Received: March 11, 2014 Accepted: April 25, 2014 Published: April 25, 2014 Article pubs.acs.org/ac © 2014 American Chemical Society 5125 dx.doi.org/10.1021/ac500903s | Anal. Chem. 2014, 86, 5125-5130