Oxygen indicators and intelligent inks for packaging food

The detection of oxygen using optical sensors is of increasing interest, especially in modified atmosphere food packaging (MAP), in which the package, usually containing food, is flushed with a gas, such as carbon dioxide or nitrogen. This tutorial review examines the ideal properties of an oxygen optical sensor for MAP and compares them with those developed to date, including the most recent advances. The basic technologies underpinning the different indicator types are described, examples given and their potential for application in MAP assessed. This tutorial review should be of interest to the MAP industry and researchers in optical sensors and oxygen sensing.     

Optimizing integrated optical chips for label-free (bio-)chemical sensing

Label-free sensing is an important method for many (bio-)chemical applications in fields such as biotechnology, medicine, pharma, ecology and food quality control. The broad range of applications includes liquid refractive index sensing, molecule detection, and the detection of particles or cells. Integrated optics based on the use of waveguide modes offers a great potential and flexibility to tailor the sensor properties to these applications. In this paper, the results of a numerical study are presented, showing that this flexibility is founded on the many degrees of freedom that can be used for the integrated optical chip design, in contrast to other technologies such as those based on surface plasmon resonance, for which the materials' properties limit the range of choices. The applications that are explicitly considered and discussed include (1) bulk refractometry, (2) thin-layer sensing, for example biosensors monitoring molecular adsorption processes occurring within some 10 nm of the chip's surface, (3) thick-layer sensing with processes involving molecules or ions to be monitored within a sensing matrix extending to some 100 nm from the chip's surface, for example hydrogel-based layers and chemo-optically sensitive membranes, and (4) particle sensing with particles or, for example, biological cells to be monitored within probe volumes extending to some 1,000 nm from the chip's surface. The peculiarities for the different types of applications will be discussed, and suitable modeling methods presented. Finally, the application-specific design guidelines supplied will enable the optimization of various types of integrated optical sensors, including interferometers and grating-based sensors.     

Design and application of stimulus-responsive droplets and bubbles stabilized by phospholipid monolayers

Biomimetic colloidal particles are promising agents for biosensing, but current technologies fall far short of Nature's capabilities for sensing, assessing, and responding to stimuli. Phospholipid-containing cell membranes are capable of binding and responding to an enormous variety of biomolecules by virtue of membrane organization and the presence of receptor proteins. By tuning the composition and functionalization of simulated membranes, soft colloids such as droplets and bubbles can be designed to respond to various stimuli. Moreover, because lipid monolayers can surround almost any hydrophobic phase, the interior of the colloid can be selected to provide a sensitive readout, for example in the form of optical microscopy or acoustic detection. In this work, we review some advances made by our group and others in the formulation of lipid-coated particles with different internal phases such as fluorocarbons, hydrocarbons, or liquid crystals. In some cases, binding or displacement of stabilizing lipids gives rise to conformational changes or disruptions in local membrane geometry, which can be amplified by the interior phase. In other cases, multivalent analytes can promote aggregation or even membrane fusion, which can be utilized for an optical or acoustic readout. By highlighting a few recent examples, we hope to show that lipid monolayers represent a versatile biosensing platform that can react to and detect biomolecules by leveraging the unique capabilities of phospholipid membranes.     

Methods to array photonic crystal microcavities for high throughput high sensitivity biosensing on a silicon-chip based platform

We experimentally demonstrate a method to create large-scale chip-integrated photonic crystal sensor microarrays by combining the optical power splitting characteristics of multi-mode interference (MMI) power splitters and transmission drop resonance characteristics of multiple photonic crystal microcavities arrayed along the length of the same photonic crystal waveguide. L13 photonic crystal microcavities are employed which show high Q values (~9300) in the bio-ambient phosphate buffered saline (PBS) as well as high sensitivity, experimentally demonstrated to ~98 atto-grams. Two different probe antibodies were specifically detected simultaneously with a control sample, in the same experiment.     

Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development

Current concepts for chemical and biochemical sensing based on detection with optical waveguides are reviewed. The goals are to provide a framework for classifying such sensors and to assist a designer in selecting the most suitable detection techniques and waveguide arrangements. Sensor designs are categorized on the basis of the five parameters that completely describe a light wave: its amplitude, wavelength, phase, polarization state and time-dependent waveform. In the fabrication of a successful sensor, the physical or chemical property of the determined species and the particular light wave parameter to detect it should be selected with care since they jointly dictate the sensitivity, stability, selectivity and accuracy of the eventual measurement. The principle of operation, the nature or the detected optical signal, instrumental requirements for practical applications, and associated problems are analyzed for each category of sensors. Two sorts of sensors are considered: those based on direct spectroscopic detection of the analyte, and those in which the analyte is determined indirectly through use of an analyte-sensitive reagent. Key areas of recent study, useful practical applications, and trends in future development of optical waveguide chemical and biochemical sensors are considered.     

Heightened sense for sensing: recent advances in pathogen immunoassay sensing platforms

Rapid and efficient sensors are essential for effective defense against the emerging threat of bioterrorism and biological warfare. This review article describes several recent immunosensing advances that are relevant to biothreat detection. These highly diverse examples are intended to demonstrate the breadth of these immunochemical sensing systems and platforms while highlighting those technologies that are suitable for pathogen detection.     

Optical biosensors based on integrated polymer light source and polymer photodiode

Evanescent coupling is used to couple light from an organic Lambertian emitter into a single‐mode planar waveguide. A polymer light emitting diode pumps a photoluminescent layer located directly on top of the waveguide. At the out‐coupling grating stage, a fully organic mini‐spectrometer compatible with monolithical integration on optical bio chips has been developed. It consists of a single‐mode waveguide with integrated diffraction grating and a dense array of polymer photodiodes as sensing element. An overall spectral resolution of down to 5 nm has been achieved with the integrated optoelectronic system. As a proof of principle the fully organic optical device has been used in combination with a fluidic system to demonstrate an absorption‐based bio‐test with mouse immunoglobulin G. In a further step towards low‐cost and disposable lab‐on‐chip biosensors, the mentioned organic building blocks have been combined with a surface plasmon stack integrated directly onto the single mode waveguide. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Integrated microring resonator sensor arrays for labs-on-chips

Planar waveguide optical ring resonators have shown great potential as compact and sensitive biochemical sensors. Advances in integrated optics based on Si technologies have allowed researchers to integrate multiple micron-sized ring resonator sensors with other optical and fluidic functions on Si chips using mass production techniques. Recent demonstrations of clinically relevant analyte detection by MRR sensor arrays have moved this technology closer to commercialization. Here, a survey of the development of microring sensor arrays for lab-on-a-chip applications is presented and illustrated with state-of-the-art examples.     

Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development

Current concepts for chemical and biochemical sensing based on detection with optical waveguides are reviewed. The goals are to provide a framework for classifying such sensors and to assist a designer in selecting the most suitable detection techniques and waveguide arrangements. Sensor designs are categorized on the basis of the five parameters that completely describe a light wave: its amplitude, wavelength, phase, polarization state and time-dependent waveform. In the fabrication of a successful sensor, the physical or chemical property of the determined species and the particular light wave parameter to detect it should be selected with care since they jointly dictate the sensitivity, stability, selectivity and accuracy of the eventual measurement. The principle of operation, the nature or the detected optical signal, instrumental requirements for practical applications, and associated problems are analyzed for each category of sensors. Two sorts of sensors are considered: those based on direct spectroscopic detection of the analyte, and those in which the analyte is determined indirectly through use of an analyte-sensitive reagent. Key areas of recent study, useful practical applications, and trends in future development of optical waveguide chemical and biochemical sensors are considered. Received: 19 January 1998 / Revised: 15 May 1998 / Accepted: 21 May 1998     

光波导二氧化氮气敏传感元件的研究

本文用离子交换法制备K+交换玻璃光波导元件,并在其表面固定纳米级敏感层酞菁铜(CuPc)薄膜,利用光波导气体检测系统对NO2气体进行测试.结果表明,该传感元件常温下对NO2等气体有快速、可逆的响应,并具有重现性好,灵敏度高等特点.     

Chromogenic and fluorogenic reagents for chemical warfare nerve agents' detection

The ease of production, the extreme toxicity of organophosphorus-containing nerve agents, and their facile use in terrorism attacks underscores the need to develop accurate systems to detect these chemicals. Among different technologies we review here recent advances in the design of chromo-fluorogenic methods for the specific detection of nerve agents. Optical sensing (especially colorimetric detection) requires usually low-cost and widely used instrumentation and offers the possibility of so-called "naked eye detection". Recent reported examples suggest that the application of chromo-fluorogenic supramolecular concepts for the chromogenic or fluorogenic sensing of nerve agents might be an area of increasing interest that would allow developing systems able to overcome some of the limitations shown by classical analytical methods.     

Developments in the production of biological and synthetic binders for immunoassay and sensor-based detection of small molecules

The need for chemical and biological entities of predetermined selectivity and affinity towards target analytes is greater than ever, in applications such as environmental monitoring, bioterrorism detection and analysis of natural toxin contaminants in the food chain.In this review, we focus on advances in the production of specific binders, in terms of both natural entities (e.g., antibodies) and synthetic binders (e.g., molecularly-imprinted polymers). We discuss the potential of emerging technologies for integration into immunoassay and sensing techniques. We place special emphasis on use of these technologies in bioanalytical applications.     

Recent advances in large-scale assembly of semiconducting inorganic nanowires and nanofibers for electronics, sensors and photovoltaics

Semiconducting inorganic nanowires (NWs), nanotubes and nanofibers have been extensively explored in recent years as potential building blocks for nanoscale electronics, optoelectronics, chemical/biological/optical sensing, and energy harvesting, storage and conversion, etc. Besides the top-down approaches such as conventional lithography technologies, nanowires are commonly grown by the bottom-up approaches such as solution growth, template-guided synthesis, and vapor-liquid-solid process at a relatively low cost. Superior performance has been demonstrated using nanowires devices. However, most of the nanowire devices are limited to the demonstration of single devices, an initial step toward nanoelectronic circuits, not adequate for production on a large scale at low cost. Controlled and uniform assembly of nanowires with high scalability is still one of the major bottleneck challenges towards the materials and device integration for electronics. In this review, we aim to present recent progress toward nanowire device assembly technologies, including flow-assisted alignment, Langmuir-Blodgett assembly, bubble-blown technique, electric/magnetic- field-directed assembly, contact/roll printing, planar growth, bridging method, and electrospinning, etc. And their applications in high-performance, flexible electronics, sensors, photovoltaics, bioelectronic interfaces and nano-resonators are also presented.     

Particles and microfluidics merged: perspectives of highly sensitive diagnostic detection

There is a growing need for diagnostic technologies that provide laboratories with solutions that improve quality, enhance laboratory system productivity, and provide accurate detection of a broad range of infectious diseases and cancers. Recent advances in micro- and nanoscience and engineering, in particular in the areas of particles and microfluidic technologies, have advanced the “lab-on-a-chip” concept towards the development of a new generation of point-of-care diagnostic devices that could significantly enhance test sensitivity and speed. In this review, we will discuss many of the recent advances in microfluidics and particle technologies with an eye towards merging these two technologies for application in medical diagnostics. Although the potential diagnostic applications are virtually unlimited, the most important applications are foreseen in the areas of biomarker research, cancer diagnosis, and detection of infectious microorganisms.

Optical leaky waveguide biosensors for the detection of organophosphorus pesticides

Organophosphorus (OP) pesticides can be rapidly detected by integrating organophosphorus hydrolase with an optical leaky waveguide biosensor. This enzyme catalyses the hydrolysis of a wide range of organophosphorus compounds causing an increase in the pH. Thus, the direct detection of OP is possible by monitoring of the pH changes associated with the enzyme's activity. This article describes the use of an optical, leaky waveguide clad with absorbing materials for the detection of OP pesticides by measuring changes in refractive index, absorbance and fluorescence. In the most effective configuration, a thick sensing layer was used to increase the amount of immobilized enzyme and to increase the light interaction with the sensing layer, resulting in a greatly enhanced sensitivity. The platforms developed in this work were successfully used to detect paraoxon and parathion down to 4 nM concentrations.     

金属腐蚀监测的光波导传感方法研究

本文提出一种用于金属腐蚀监测的光波导传感方案 ,用金属膜层局部取代光波导的介质包层 ,构成腐蚀敏感膜 ,从而获取金属腐蚀信息 .依据波导理论选用 72 1比色皿上的石英玻璃作为光波导材料 ,利用电化学方法在波导材料内表面上形成Fe C合金腐蚀敏感膜 ,并用XRD、EDX等对膜层结构进行分析 .在电化学腐蚀膜的同时 ,用光学方法记录光波导输出光功率的变化 ,实验结果表明电化学方法与光学方法获取的腐蚀信息同步 ,证实了所提传感方案可行     

光波导传感元件在检测酸性气体中的应用

采用旋转甩涂法将甲基紫传感薄膜固定在特制的锡(Sn2+,Sn4+)掺杂玻璃光波导(Sn doped glass slide)表面,研究了该传感薄膜与HCl、H2S、以及SO2作用前后的可见吸收光谱的变化,并在此基础上研制了玻璃光波导酸性气体(HCl、H2S、SO2)传感元件。传感薄膜与酸性气体作用时,薄膜的颜色发生变化,从而降低薄膜对倏逝波的吸收,使传感器的输出光强度(信号)增强。本文采用流动注射法对酸性气体进行了检测。实验结果表明,在室温下,该传感元件对硫化氢气体具有明显的响应,而对相同浓度的其他酸性气体的响应相对较小,对浓度在6×10-4～2.5×10-5(V/V)的硫化氢气体具有良好的线性响应(R=0.9979,n=4),相对标准偏差(RSD)为±3.5%,具有响应快、可逆性和重复性好、容易制备、可以在室温下工作等特点。     

Tailorable integrated optofluidic filters for biomolecular detection

Spectral filtering is an essential component of biophotonic methods such as fluorescence and Raman spectroscopy. Predominantly utilized in bulk microscopy, filters require efficient and selective transmission or removal of signals at one or more wavelength bands. However, towards highly sensitive and fully self-contained lab-on-chip systems, the integration of spectral filters is an essential step. In this work, a novel optofluidic solution is presented in which a liquid-core optical waveguide both transports sample analytes and acts as an efficient filter for advanced spectroscopy. To this end, the wavelength dependent nature of interference-based antiresonant reflecting optical waveguide technology is exploited. An extinction of 37 dB, a narrow rejection band of only 2.5 nm and a free spectral range of 76 nm using three specifically designed dielectric layers are demonstrated. These parameters result in an 18.4-fold increase in the signal-to-noise ratio for on-chip fluorescence detection. In addition, liquid-core waveguide filters with three operating wavelengths were designed for F?rster resonance energy transfer detection and demonstrated using doubly labeled oligonucleotides. Incorporation of high-performance spectral processing illustrates the power of the optofluidic concept where fluidic channels also perform optical functions to create innovative and highly integrated lab-on-chip devices.     

Intrinsic UV absorption spectrometry observed with a liquid core waveguide as a sensor technique for monitoring ozone in water

The industrial use of ozone as a sanitizing agent in water treatment and food processing in recent years calls for sensor technologies for monitoring ozone in water for process control. Ozone molecules absorb UV light with a peak absorption wavelength at 254 nm. This property has been used in this work to develop a simple sensor technology for online, real-time continuous monitoring of trace ozone in water. A Teflon AF2400 tube filled with pure water forms a liquid core waveguide (LCW), which is used as a long-path-length optical absorption cell. This pure water filled tube was deployed into a water sample. Ozone molecules dissolved in the water sample permeate through the Teflon AF2400 tube wall and dissolve in water filled in the tube. This prevents interference species from entering the LCW, and eliminates interferences. The optical absorption signal of the long-path-length cell at 254 nm measured by guiding light through the LCW is used as a sensing signal. This simple structured sensor does not involve any chemical reagent, is reversible, and has a response time <4.5 minutes. It can be used to detect ozone in water samples down to 3.6 × 10(-9) mol L(-1).     

Optical filtering technologies for integrated fluorescence sensors

Numerous approaches have been taken to miniaturizing fluorescence sensing, which is a key capability for micro-total-analysis systems. This critical, comprehensive review focuses on the optical hardware required to attenuate excitation light while transmitting fluorescence. It summarizes, evaluates, and compares the various technologies, including filtering approaches such as interference filters and absorption filters and filterless approaches such as multicolor sensors and light-guiding elements. It presents the physical principles behind the different architectures, the state-of-the-art micro-fluorometers and how they were microfabricated, and their performance metrics. Promising technologies that have not yet been integrated are also described. This information will permit the identification of methods that meet particular design requirements, from both performance and integration perspectives, and the recognition of the remaining technological challenges. Finally, a set of performance metrics are proposed for evaluating and reporting spectral discrimination characteristics of integrated devices in order to promote side-by-side comparisons among diverse technologies and, ultimately, to facilitate optimized designs of micro-fluorometers for specific applications.