Current-Based High-Sensitivity Differential Detection of Light Power Using Si Photodiodes in Bridge Configuration for Chemical/Biological Optical Sensing☆

Abstract We present a new optoelectronic technique based on the differential measurement of currents for the detection of the variations of low concentrations of chemical and biological substances by measuring light power absorption through two Si-photodiodes (SiPD) in a bridge configuration. The solution exhibits high sensitivity, linear response and allows the compensation of the initial bridge unbalance without changing its elements so optimising signal amplification gain and detection resolution. The technique shows unique performances with respect to voltage amplitude measurements performed by lock-in amplifiers. Moreover, the experimental apparatus is simple and suitable for portable integrated sensor systems. Its main performances have been evaluated through a prototype PCB demonstrating the capability to detect light power variations with a settable maximum sensitivity of 30mV/nW and a resolution of 33pW

Low-cost Discrete Off-the-shelf Components 1MHz Analogue Lock-in Amplifier for Fast Detection of Organic Compounds through Pulsed Lasers

Abstract We report on a low-cost analogue Lock-In Amplifier (LIA) designed to measure amplitude variations of 100 ns pulsed signals at operating frequencies f 0 up to 1MHz. The fabricated prototype PCB, implemented through discrete off-the-shelf components, allowed to validate the solution and to perform circuit testing and characterisations. The LIA architecture is simple and based on the classic phase-sensitive synchronous demodulation technique including two different amplification stages together with suitable filtering blocks that allow setting the instrument gain, sensitivity and resolution. With respect to conventional LIAs typically working at lower operating frequencies, the reported solution provides also high-speed DC output of about 1ms. By employing short voltage pulses, the LIA is capable to detect fast and small variations of the signal amplitude envisaging its use in sensor applications to measure reduced variations of chemical and physical phenomena through high-speed systems with very small time constants

Meso-scale fluidic devices with chemical sensors for biological applications

Molecular oxygen and humidity are some of the major environmental quantities being measured for various industrial and commercial applications. This dissertation focuses on the design, fabrication and characterization of optofluidic biosensor systems for oxygen and humidity quantification using color charge-coupled device (CCD) camera as a photodetector and LED panel as an excitation source. Meso-scale fluidic devices with integrated oxygen and humidity sensors for potential applications to hydrotropic and oxytropic studies of small plant roots have been investigated in this study. Meso-scale sensor platform was fabricated using porphyrine complex as the sensitive dye embedded within Ethyl Cellulose (EC) polymer matrix. Green LED light displayed from the light panel helped in exciting the oxygen complex by emitting varied fluorescence emission corresponding to oxygen. This method of optical oxygen imaging helps in wide area distribution over the sensor platform. The root tip response to environmental stimuli by directed growth plays a major role in plant development. With these tropic responses of roots, plants can help themselves during environmental risks such as drought conditions. Different fluidic devices were fabricated with embedded humidity sensors within the device to study the effect of tropic responses. Hydrotropic behavior of corn roots was analyzed along with humidity gradient quantification using color charge-coupled device (CCD) camera for both imaging of the plant root and profiling of humidity distribution. Successfully created and analyzed the humidity gradient which resulted in root orientation because of hydrotropic response indicating the effectiveness of this device for further biological applications --Abstract, page iv

Characterisation and optimisation of novel Sol-Gel materials for luminescence-based 02 sensing

Current sensor trends, such as multi-analyte measurement, miniaturisation and printability, are important drivers for materials to be used in optical chemical sensors. In recent years, there has been a focus on sol-gel materials for sensor applications due to their excellent optical properties, ease of entrapment of analyte-sensitive dyes and the compatibility of the sol-gel process with a range of deposition techniques. This study focuses on the fabrication, characterisation and optimisation of novel sol-gel ORMOSIL (ORganically MOdified SILicate) matrices for luminescence-based O2 sensing. The O2 sensing scheme is based on the luminescence quenching of the highly 0 2 - sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-l,10-phenanthroline) dichloride], entrapped in a porous sol-gel film. A phase fiuorometric detection scheme was employed which capitalised on the inherent advantages of frequency-domain rather than time- or intensity-domain measurements. This study focuses on optimisation of the O2 sensor response under a variety of headings including, sensitivity, dynamic range, photobleaching effects and sensor interferences caused by solvent vapour. Key film parameters include porosity and film hydrophobicity. These parameters are intimately related to the precursors used, in addition to sol-gel processing parameters. The xerogel microstructure was investigated using spectroscopic ellipsometry. 0 2 diffusion coefficients were also measured and the results were correlated to porosity and sensor sensitivity data. A study of the phase fiuorometric response as a function of LED modulation frequency highlighted the importance of optical filter selection in order to produce the optimum sensor response. It is clear from this work that the O2 sensitivity of the film can be tailored via the sol-gel precursor used. Furthermore, there is a general correlation between the hydrophobicity of the film and the length of the precursor alkyl chain. Good correlation was obtained between porosity, diffusion coefficient and O2 sensing data. Finally, the work highlights the versatility of the sol-gel route to provide application-specific materials, thereby providing solutions to a variety of sensing problems

Methodology for phytoplankton taxonomic group identification towards the development of a lab-on-a-chip

This paper presents the absorbance and fluorescence optical properties of various phytoplankton species, looking to achieve an accurate method to detect and identify a number of phytoplankton taxonomic groups. The methodology to select the excitation and detection wavelengths that results in superior identification of phytoplankton is reported. The macroscopic analyses and the implemented methodology are the base for designing a lab-on-a-chip device for a phytoplankton group identification, based on cell analysis with multi-wavelength lighting excitation, aiming for a cheap and portable platform. With such methodology in a lab-on-a-chip device, the analysis of the phytoplankton cells’ optical properties, e.g., fluorescence, diffraction, absorption and reflection, will be possible. This device will offer, in the future, a platform for continuous, autonomous and in situ underwater measurements, in opposition to the conventional methodology. A proof-of-concept device with LED light excitation at 450 nm and a detection photodiode at 680 nm was fabricated. This device was able to quantify the concentration of the phytoplankton chlorophyll a. A lock-in amplifier electronic circuit was developed and integrated in a portable and low-cost sensor, featuring continuous, autonomous and in situ underwater measurements. This device has a detection limit of 0.01 µ/L of chlorophyll a, in a range up to 300 µg/L, with a linear voltage output with chlorophyll concentration.European Regional Development Fund (ERDF) through the Interreg VA Spain-Portugal (POCTEP) 2014–2020 Program under grant agreement 0591_FOODSENS_1_E, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020, and by project NORTE-08-5369-FSE-000039 co-founded by the European Social Fund FSE and through National funds NORTE 2020 and Regional Operacional Programa of North 2014/2020. The University of Vigo work was funded by a Xunta de Galicia grant to the Biological Oceanography Research Group (Consolidación e estruturación de unidades). This output reflects only the views of the authors, and the program authorities cannot be held responsible for any use that may be made of the information contained therei

Methodology for phytoplankton taxonomic group identification towards the development of a lab-on-a-chip

This paper presents the absorbance and fluorescence optical properties of various phytoplankton species, looking to achieve an accurate method to detect and identify a number of phytoplankton taxonomic groups. The methodology to select the excitation and detection wavelengths that results in superior identification of phytoplankton is reported. The macroscopic analyses and the implemented methodology are the base for designing a lab-on-a-chip device for a phytoplankton group identification, based on cell analysis with multi-wavelength lighting excitation, aiming for a cheap and portable platform. With such methodology in a lab-on-a-chip device, the analysis of the phytoplankton cells’ optical properties, e.g., fluorescence, diffraction, absorption and reflection, will be possible. This device will offer, in the future, a platform for continuous, autonomous and in situ underwater measurements, in opposition to the conventional methodology. A proof-of-concept device with LED light excitation at 450 nm and a detection photodiode at 680 nm was fabricated. This device was able to quantify the concentration of the phytoplankton chlorophyll a. A lock-in amplifier electronic circuit was developed and integrated in a portable and low-cost sensor, featuring continuous, autonomous and in situ underwater measurements. This device has a detection limit of 0.01 µ/L of chlorophyll a, in a range up to 300 µg/L, with a linear voltage output with chlorophyll concentration.Fundação para a Ciência e a Tecnologia | Ref. UIDB/04436/2020Fundação para a Ciência e a Tecnologia | Ref. UIDP/04436/2020Fundação para a Ciência e a Tecnologia | Ref. PD/BD/150581/2020Fundação para a Ciência e a Tecnologia | Ref. 2021.01087.CEECINDFundação para a Ciência e a Tecnologia | Ref. 2021.01086.CEECIN

State-of-the-Art of (Bio)Chemical Sensor Developments in Analytical Spanish Groups

(Bio)chemical sensors are one of the most exciting fields in analytical chemistry today. The development of these analytical devices simplifies and miniaturizes the whole analytical process. Although the initial expectation of the massive incorporation of sensors in routine analytical work has been truncated to some extent, in many other cases analytical methods based on sensor technology have solved important analytical problems. Many research groups are working in this field world-wide, reporting interesting results so far. Modestly, Spanish researchers have contributed to these recent developments. In this review, we summarize the more representative achievements carried out for these groups. They cover a wide variety of sensors, including optical, electrochemical, piezoelectric or electro-mechanical devices, used for laboratory or field analyses. The capabilities to be used in different applied areas are also critically discussed

Nanoparticle- and microparticle-based luminescence imaging of chemical species and temperature in aquatic systems: a review

© 2019, Springer-Verlag GmbH Austria, part of Springer Nature. Most aquatic systems rely on a multitude of biogeochemical processes that are coupled with each other in a complex and dynamic manner. To understand such processes, minimally invasive analytical tools are required that allow continuous, real-time measurements of individual reactions in these complex systems. Optical chemical sensors can be used in the form of fiber-optic sensors, planar sensors, or as micro- and nanoparticles (MPs and NPs). All have their specific merits, but only the latter allow for visualization and quantification of chemical gradients over 3D structures. This review (with 147 references) summarizes recent developments mainly in the field of optical NP sensors relevant for chemical imaging in aquatic science. The review encompasses methods for signal read-out and imaging, preparation of NPs and MPs, and an overview of relevant MP/NP-based sensors. Additionally, examples of MP/NP-based sensors in aquatic systems such as corals, plant tissue, biofilms, sediments and water-sediment interfaces, marine snow and in 3D bioprinting are given. We also address current challenges and future perspectives of NP-based sensing in aquatic systems in a concluding section. [Figure not available: see fulltext.]