Environmental Monitoring Ajeet Kaushik,*,†,‡ Rajesh Kumar,*,‡,§ Sunil K. Arya, Madhavan Nair,† B. D. Malhotra, and Shekhar Bhansali‡ †Center for Personalized Nanomedicine, Institute of Neuroimmune Pharmacology, Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida 33199, United States ‡Bio-MEMS Microsystems Laboratory, Department of Electrical and Computer Engineering, College of Engineering, Florida International University, Miami, Florida 33174, United States Department of Physics, Panjab University, Chandigarh 160014, India Bioelectronics Program, Institute of Microelectronics, A*Star, 11 Science Park Road, Singapore Science Park II, Singapore Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India

Organic–Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring

During the last decade there has been a rapidly growing interest in integrated optical (IO) sensors, expecially because many of them principally allow for sensitive, real time, label-free-on-site measurements of the concentration of (bio-)chemical species. This review aims at giving an overview of the most relevant developments in this area. After a general introduction into the field of IO sensors for the chemical domain, relevant aspects of integrated optics and chemical sensing are presented in short. A large variety of IO sensing platforms are introduced and discussed: interferometers, resonators, coupling-based devices such as grating couplers and surface plasmon resonance based sensors and finally a new class of sensors based on chemically induced field profile changes. Strong and weak points of principle and of configuration based on these principles are indicated and the main performance data of the IO sensing platforms, especially the obtained resolution, are indicated. Best resolutions of the chemically induced refractive indices on the order of magnitude $10^{-6}-10^{-8}RIU$ can be obtained, corresponding to a resolution of $10^{-3}-10^{-5}$nm in the chemically induced growth of layer thickness of chemo-optical transducer materials. Depending on the anlalyte and the type of transduction layer chemical concentrations down to some ppb or some pg $ml^{-1}$can be determined. Several IO sensing systems are commercially available. Extension of individual sensors to sensor arrays is treated and finally an outlook for the future is given.

Integrated Optical sensors for the chemical domain

Block Copolymer-Based Supramolecular Ionogels for Accurate On-Skin Motion Monitoring

In this work, an optical humidity sensor based on a nanoporous polymeric photonic crystal (PC) is demonstrated. The PC sensing structure is created by combining a holographic interference patterning technique with a modified holographic polymer-dispersed liquid crystal system. Changes in relative humidity (RH) induce the modification of the refractive index contrast between the nanoporous and nonporous regions, and thus the transmittance and bandgap position, of the PC structure. For a PC structure with 30% porosity and a grating spacing of 220 nm, a change in the RH from 40% to 95% at 34 °C results in a redshift of 43 nm in the central wavelength at the PC bandgap and an increase from 12% to 87% in the relative transmittance at λ = 600 nm. Other performance analyses have shown that the nanoporous polymeric PC-based humidity sensor is highly stable and reproducible, exhibits minimal hysteresis, and responds relatively fast.

Humidity sensing based on nanoporous polymeric photonic crystals

A Fabry–Perot micro-optical sensing resonator fabricated by direct laser writing on the endface of a standard telecom fiber is demonstrated. This endface optical fiber sensing probe has been tested for tracing the vapors of common organic solvents. The device operates in the spectral region lying between 1440 and 1660 nm, while the spectra recorded in reflection mode correlate to the refractive index changes due to the different vapors trapped inside the microcavity. The performance of the device operation with respect to the reflecting surface porosity of the fabricated microstructure is presented, while the sensing of ethanol traces down to 4 ppm concentrations was achieved.

A Fiber-Endface, Fabry–Perot Vapor Microsensor Fabricated by Multiphoton Polymerization

Efficient functionalization of polymer optical fibers' (POF) surface by a novel block copolymer material toward the development of low-cost multiagent sensors is presented. The employed poly(styrene sulfonate-b-tert-butylstyrene) (SPS-b-PtBS) diblock copolymer possesses two blocks of distinctively different polarity and charge, the hydrophilic SPS which is sensitive to polar substances and the hydrophobic PtBS which is sensitive to organic solvents. The coexistence of two different blocks allows for the detection of a wide variety of agents, ranging from ammonia, and organic solvents, to biomolecules like lysozyme, at room temperature as opposed to alternative usually more complicated techniques, all with the sole use of one sensing medium. Copolymers' high glass transition temperature enables the formation of stable and environmentally robust overlayers. The sensing performance of the material is evaluated experimentally on the customizable platform of POFs, demonstrating fast response, high operational reversibility, and also reusability in successively different testing agents. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 46–54

/pdf/amphiphilic-diblock-copolymer-based-multiagent-photonic-4tu3u7dqv4.pdf

Amphiphilic diblock copolymer‐based multiagent photonic sensing scheme

Remote-point photonic sensors are fabricated and evaluated. They are based on nanocomposite thin films comprising NiCl2 nanocrystals embedded in sol-gel silica matrix and are patterned using direct UV laser microetching techniques to form surface relief structures, which exhibit environment sensitive optical diffraction effects. A strong response to ammonia is detected via the alteration of diffraction efficiency of its orders upon exposure to the analyte. Detection of ammonia in the 2 ppm level with a typical response time of about 30 s in the ambient, 50% RH 20°C, room environment is demonstrated.

pdf/diffractive-optic-sensor-for-remote-point-detection-of-51feitfs40.pdf

Diffractive optic sensor for remote-point detection of ammonia.

A study of polymer optical fiber microstructuring by use of deep ultraviolet excimer laser radiation at 193 nm wavelength is performed. The ablation characteristics of the fiber cladding and core materials are analyzed comparatively. The laser irradiation effects are dynamically studied by on-line monitoring of the laser ablation induced waveguiding losses, the latter being correlated with the spatial structuring parameters. The fiber surface is modified to incorporate cavities, which are subsequently employed as sensitive material receptors for the development of customized photonic sensors. The sensing capability of the microstructured plastic optical fibers is demonstrated by ammonia and humidity detection.

http://iopscience.iop.org/article/10.1088/2040-8978/17/1/015402/pdf

ArF excimer laser microprocessing of polymer optical fibers for photonic sensor applications

The use of lossless optical media exhibiting reversible optical interactions upon exposure to physical and chemical agents allows for the implementation of remote point photonic sensors. Hybrid nanocomposite media represent a new class of sensor materials. They are produced by flexible chemical synthesis methods and can potentially be tailored by design to implement specific functionalities. These materials combined with externally manipulated optical interfaces lead to an emerging class of diffractive photonic devices offering unique sensing potential and advantageous operational features at low cost. The first case studies on ammonia and methanol detection are discussed.

Nanocomposite hybrid photonic media for remote point sensors

Diffractive Ammonia Sensors Based on Sol–Gel Nanocomposites Materials

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