Optical Transduction Techniques Research Articles

Emerging Biosensing Technologies towards Early Sepsis Diagnosis and Management.

Sepsis is defined as a systemic inflammatory dysfunction strictly associated with infectious diseases, which represents an important health issue whose incidence is continuously increasing worldwide. Nowadays, sepsis is considered as one of the main causes of death that mainly affects critically ill patients in clinical settings, with a higher prevalence in low-income countries. Currently, sepsis management still represents an important challenge, since the use of traditional techniques for the diagnosis does not provide a rapid response, which is crucial for an effective infection management. Biosensing systems represent a valid alternative due to their characteristics such as low cost, portability, low response time, ease of use and suitability for point of care/need applications. This review provides an overview of the infectious agents associated with the development of sepsis and the host biomarkers suitable for diagnosis and prognosis. Special focus is given to the new emerging biosensing technologies using electrochemical and optical transduction techniques for sepsis diagnosis and management.

Functionalized SERS substrate based on silicon nanowires for rapid detection of prostate specific antigen

Abstract Owing to its high sensitivity, surface-enhanced Raman spectroscopy (SERS) is widely used in biosensing as an efficient optical transduction technique. In this work, we report the elaboration of a novel SERS-powered aptasensing substrate for the ultra-sensitive and selective detection of prostate specific antigen (PSA). The transducing SERS substrate is formed by vertically aligned silicon nanowires (SiNWs) decorated with silver nanoparticules (AgNPs). The silver nanoparticles have two purposes : a) aptamer immobilization via thiol chemistry and b) Raman signal enhancement. The presence of PSA induces the appearance of amide bond vibration modes only if the aptamer is present on the surface of SiNWs. The platform is highly sensitive, selective and specific to PSA in a wide range of concentrations from 0.1 to 20 μg.L−1 with a detection limit of 0.1 μg.L−1, which encompasses the blood serum range of healthy subjects and ill patients. This optical biosensor shows a great stability and it is successfully validated in human blood serum samples showing very good results.

Recent advances in the metamaterial-inspired biosensors

Metamaterials (MM)-inspired microwave biosensors are a valuable addition to the field of diagnostic approaches and prognostic tools. The fundamental principle behind these biosensors is unique dielectric signatures corresponding to healthy/diseased tissues. Relying on nonionizing radiation and offering an increased resolution with accuracy comparable to that of ultrasound devices, they are an attractive solution for noninvasive and label-free biosensing applications. High-quality-factor MM-inspired resonators are integrated with microfluidics to accelerate the lab-on-chip and point-of-care diagnostic approaches owing to the small detection volume and overall compact size of these devices. A variety of biomolecular detection, glucose detection and hyperthermia treatment using state-of-the-art MM-inspired biosensors have been discussed. Optical transduction techniques (e.g., surface plasmon resonance) which enhance the sensitivity in terms of limit-of-detection and resolution, have also been outlined. Utilization of microwave biosensors as therapeutic agents is at its initial stages owing to lack of required sensitivity and reliability in recently proposed MM-inspired biosensors.

SensLED: An Electro‐Optical Active Probe for Oxygen Determination

Adv. Mater. 2009, 21, 3483–3487 2009 WILEY-VCH Verlag G Optical sensors have been a field of intensive academic as well as industrial research over the last three decades. Clark-type electrodes, for example, have been a standard for many years in oxygen detection; however, they are more andmore replaced by optical sensors. Different optical sensor systems, e.g., fiber optic or planar waveguide based platforms, were developed using the optical properties of the analyte itself as well as changes of the optical properties of an intermediate indicator molecule (e.g., organometallic compounds) for analyte detection. To yield analyte information, most common optical transduction techniques used in optical chemical sensors are based on fluorescence or absorption measurements (e.g., nondispersive infrared sensors). In this context, the class of so-called direct sensors uses a modification of an intrinsic optical property of the analyte, whereas in the case of inappropriate intrinsic optical properties an intermediate analyte-sensitive dye molecule has to be added. The presence of the corresponding analyte alters the optical properties of the indicator dye, thus allowing its detection. Such a sensing technique requires, depending on the phase of the analyte, in most cases an immobilization of the dye within a matrix layer, which provides analyte accessibility but prevents leaching effects. Different approaches for immobilization of indicators within a matrix material have been realized up to now, such as covalent bonding or simple encapsulation. Apart from analyte diffusion coefficients within the matrix, sensitivity as well as sensor response time strongly depend on indicator– matrix interactions. Due to these interactions, spectroscopic shifts and enhanced or reduced excited state lifetimes are frequently observed in the solid state compared to solution. Nevertheless, embedding the dye molecule within a rigid matrix enhances the photostability due to reduced ligand photodegradation. Along this line, optical oxygen probes commonly use platinum or palladium based organometallic complexes as indicator molecules. Spin orbit coupling is enhanced because of the metal ion within the organic complex; this enables an efficient radiative decay from the lowest triplet state to the singlet ground state of the molecule (phosphorescence). Because spin orbit coupling is weak in fluorescent materials, a radiative decay from an excited triplet state is unlikely. The phosphorescence lifetime of organometallic complexes is, depending on the transient metal complex and the matrix material, in the range of microseconds, which is several orders of magnitude larger than the fluorescent excited state lifetime. Most reagent-mediated optical oxygen sensors use dynamic interactions between the excited state of the dye molecule and the analyte. Since molecular contact is required for this kind of interaction, the analyte has to reach the immobilized dye molecule within its excited state lifetime. Taking into consideration the physical parameters of the matrix material, e.g., diffusion coefficients, the lifetime determines the maximum distance that an analyte molecule can move to reach and interact with an excited indicator molecule. The quenching probability is therefore higher than that of fluorescent emitters, because of the enhanced lifetime of transient metal complexes. Hence, the lifetime of the excited molecule state is an important aspect of sensor performance as well as a determining factor for the complexity of the measurement equipment. An excited state lifetime in the range of microseconds, as common for most transient metal complexes, allows the use of low-cost electronics for lifetime determination, which is an inherent advantage of this class of materials over fluorescent indicators. In electro-optical devices, simple spin statistics predict that 75% of the injected charges form triplet excitons, whereas only 25% are in the singlet state. However, various studies presented in the past suggest variation in the singlet–triplet exciton ratios, which was also confirmed by quantum mechanical calculations and enhanced electroluminescence quantum yield (ELQY). Nevertheless, later studies claim that the ELQYof organic light-emitting devices is restricted to the spin statistics meaning that only a 25% singlet yield can be obtained. Therefore, in order to harvest a maximum amount of emissive exciton recombination, phosphorescent complexes are commonly used to improve the overall EL output by enhancing the

A Mach-Zehnder interferometer based on silicon oxides for biosensor applications

Integrated optical devices have been increasingly interested in biosensor applications including environmental pollution, biological process and medical diagnostics. Integrated optics allows high-detection sensitivity to be achieved using optical transduction techniques in a microfluidic format. Among different transduction techniques, a Mach-Zehnder interferometer (MZI) has advantage of its inherent high sensitivity and accuracy. The evanescent wave of an optical waveguide interacts with an adjacent layer, and this can be the basis of the recognition of biomolecules. In recent years, silicon dielectrics as potential materials have been attracted in an integrated optics. The refractive index of these silicon-based materials can be easily adjusted continuously over a wide range between 1.45 (SiO 2) and 1.97 (SiO). This comes to be very attractive in terms of design and fabrication of single-mode waveguides. In this article, we tried to realize the Mach-Zehnder interferometer sensor based on silicon oxides, and the refractive index of the oxides was controlled by the oxygen concentration to achieve the single-mode behavior of a total internal reflection (TIR) waveguide. We have performed to verify the feasibility of the MZI sensor for the direct detection of immunoreactions.

The specific molecular identification of life experiment ( SMILE)

We describe a compact, highly integrated instrument concept for the detection and identification of a wide range of molecules associated with extinct/extant life or potential life processes. The Specific Molecular Identification of Life Experiment ( SMILE) will be sensitive to the presence of a range of target molecules using both electrical and optical transduction techniques, and incorporates molecular imprinted polymers in addition to traditional biological receptors such as antibodies. A number of versions of the concept are possible depending on available resources e.g. mass, volume, etc. The full concept utilises a novel imaging interferometer where a large number of molecular receptors are deposited on the measurement plane of an imaging interferometer and read out by an imaging detector, enabling multiple targets—biomarkers—within a sample to be measured simultaneously. The optics can also form the basis of an UV–NIR imaging Fourier spectrometer allowing basic mineralogy studies to be conducted using optical properties to assist in the determination of the geological context of the samples. By incorporating micro-fabricated transducer arrays, micro-fluidics and artificial molecular recognition systems, as well as recombinant antibody technology with appropriate integration methods, SMILE forms a compact and robust “Life Marker Chip” which has been proposed for future planetary missions including ESA's ExoMars mission, where the instrument offers the possibility of conducting a direct in situ search for signs of past or present biological activity on Mars. In addition to its role in planetary exploration, derivatives of SMILE have multiple terrestrial applications in fields such as forensic analysis and environmental monitoring.

Investigation on alcohol vapours/TiO 2 nanocrystal thin films interaction by SPR technique for sensing application

Surface plasmon resonance (SPR) was explored as optical transduction technique for monitoring the response of TiO 2 thin films as sensing layers for alcohol vapours. Organic solutions of surfactant-capped TiO 2 nanocrystals were prepared by means of a colloidal chemistry route, and used as precursors for depositing the sensing layer onto Au/glass substrates. The sensing properties of the active material were examined in relation to the morphological features of both as-deposited and thermally annealed films and to the presence of the organic passivating shell on the TiO 2 nanocrystals surface. Untreated titania thin films exhibited a high and reproducible SPR response to alcohol vapours than the corresponding organic-free material. A beneficial role in the sensing process may therefore be attributed to the organic passivating layer on the nanocrystals surface.

Remote optical detection using microcantilevers

The feasibility of microcantilever-based optical detection is demonstrated. Microcantilevers may provide a simple means for developing single-element and multielement infrared sensors that are smaller, more sensitive, and lower in cost than quantum well, thermoelectric, or bolometric sensors. Here we specifically report here on an evaluation of laboratory prototypes that are based on commercially available microcantilevers, such as those used in atomic force microscopy. In this work, optical transduction techniques were used to measure microcantilever response to remote sources of thermal energy. The noise equivalent power at 20 Hz for room temperature microcantilevers was found to be approximately 3.5 nW/√Hz, with a specific detectivity of 3.6×107 cm Hz1/2/W, when an uncoated microcantilever was irradiated by a low-power diode laser operating at 786 nm. Operation is shown to be possible from dc to kHz frequencies, and the effect of cantilever shape and the role of absorptive coatings are discussed. Finally, spectral response in the midinfrared is evaluated using both coated and uncoated microcantilevers.