Design features for enhancing optical detection on lab-on-a-disc platforms

Centrifugal microfluidics has undergone a massive growth surge over the past 15 years, evident by the number of comprehensive reviews currently available, with special regard towards Lab-On-A-Disc (LOAD) diagnostic solutions.1–3 The potential of a LOAD system is dependent on its ability to mimic the specific laboratory protocols with which are required to conduct sample-to-answer analysis. This would include sample handling and manipulation (such as mixing and separation), sample modification (including heating and redox reactions), as well as reaction detection (such as optical, electrochemical, or as required by user). Optical detection strategies on LOAD platforms has been largely successful in both the fields of biological and chemical sensing.4 Herein, will demonstrate the optical optimisations which were carried out on a biological fluorescent-based5 and a chemical absorbance-based6 LOAD detection platforms. This will include the identification and optimisation of LED-photodiode selection, the effects of detection orientation and pathway-length fluorophore selection. Also covered will be a comparison between the microfluidic architecture for incorporating either detection methods as well as their reported limits of detection

A novel optical sensing lab-on-a-disc platform for chromium speciation

The determination chromium speciation in the field is a significant analytical challenge. While chromium exists in oxidation states from 0 to VI, it is predominantly found in the (III) and (VI) states [1]. Industry effluent (e.g. textile/electroplating) is a common source of chromium pollution in the environment. Due to corrosion inhibitors used in pipes, and contamination leaching from sanitary landfills, drinking water supplies can become contaminated also [2]. The bioavailability and toxicity of chromium is largely dependent the oxidation state of the element [2]. Consumption of Cr (III) is an essential component in human diet, as it is responsible for maintaining glucose, lipid and protein metabolism [3]. In contrast, Cr (VI) is strongly oxidizing, exhibiting high toxicity, with carcinogenic and mutagenic properties [4]. It is recommended by the World Health Organisation (WHO) that the maximum allowable concentration of chromium (VI) in drinking water is 0.05 mg L−1 [5]. Handheld colourimeters for on-site measurements are a convenient option for frequent water monitoring; however the limit of detection (LOD) of these devices is typically higher than the recommended limit. Microfluidic ‘lab-on-a-disc’ technologies were used in the development of an optical sensor for chromium speciation in water. The principal behind these devices is to minimize laboratory processes onto a microfluidic system that can be brought to the sampling site for rapid sample-to-answer analyses. The objective for this device was to design and fabricate a fully integrated optical sensor for on-site measurement of both trivalent and hexavalent chromium in freshwater. A strong focus was placed on maximizing sensitivity in order to achieve a low LOD

Changes in Intraocular Pressure with Use of Periocular Triamcinolone Cream

Purpose: To evaluate the effect of periocular topical triamcinolone cream on intraocular pressure. Methods: A retrospective chart review identified 57 patients, 114 eyes using triamcinolone cream (0.1%, 0.025%) with subsequent intraocular pressure (IOP) checks at three follow-up visits. Descriptive, univariate, and multivariate analyses were performed to assess effects of age, therapy duration, consecutive weeks on steroid, prescription strength, time of day, and method of measurement on IOP levels. Generalized Estimating Equations were used in regression models to account for correlation of eyes within subjects and across visits. Results: We identified 57 patients using triamcinolone cream for allergic or eczematous dermatitis of the eyelid. Prescription strengths were 0.025% or 0.1% and patients were followed for a median of 4.9 months. Measurements of IOP at baseline did not change as compared to all IOP measurements at follow-ups and did not change with steroid strength. The mean change in IOP at all follow-up visits was 0.07 mm Hg (95% confidence interval [CI]: –0.36, 0.50). After adjustment for the method of tonometer and the patient’s age, the mean change was 0.03 mm Hg (95% CI: –0.68, 0.73, P = 0.93). Prescription strength and consecutive weeks of therapy were not associated with IOP. Two patients experienced a significant elevation in IOP of >10 mm Hg, one through the concomitant consequences of systemic corticosteroids usage and the other through prolonged topical application. Conclusion: In patients taking periocular triamcinolone cream, there was no clinically meaningful change in mean IOP between baseline and follow-up visits, and IOP measurements were not related to variances in prescription strength or duration of therapy

A Spiking Neural Network Model of the Medial Superior Olive Using Spike Timing Dependent Plasticity for Sound Localization

Sound localization can be defined as the ability to identify the position of an input sound source and is considered a powerful aspect of mammalian perception. For low frequency sounds, i.e., in the range 270 Hz–1.5 KHz, the mammalian auditory pathway achieves this by extracting the Interaural Time Difference between sound signals being received by the left and right ear. This processing is performed in a region of the brain known as the Medial Superior Olive (MSO). This paper presents a Spiking Neural Network (SNN) based model of the MSO. The network model is trained using the Spike Timing Dependent Plasticity learning rule using experimentally observed Head Related Transfer Function data in an adult domestic cat. The results presented demonstrate how the proposed SNN model is able to perform sound localization with an accuracy of 91.82% when an error tolerance of ±10° is used. For angular resolutions down to 2.5°, it will be demonstrated how software based simulations of the model incur significant computation times. The paper thus also addresses preliminary implementation on a Field Programmable Gate Array based hardware platform to accelerate system performance

Development of an autonomous algal toxin analytical platform for aquatic monitoring

Cyclic peptide cyanobacterial toxins, in particular Microcystis aeruginosa, pose a serious health risk to humans and animals alike [1], [2]. Occurring mostly in fresh and brackish water, they have been identified to cause cancer promotion and liver damage [3]. Herein, we describe a portable, microfluidic-based system for in-situ detection of algal toxins in fresh water. The technology development presented here is a fully integrated and portable sample-to-answer centrifugal microfluidics-based system for the detection of toxic cyanobacteria – Microcystin-LR in fresh water. Our unique system employs highly-specific recombinant chicken anti-microcystin antibodies, prepared in-house, with a 3D-printed ‘LASER-photo¬diode’ fluorescent detection technique, also developed in-house. The system has high analytical specificity and sensitivity for detection of toxins below the regulatory limit with intra/inter day coefficient of variation of less than 20%. Dissolvable-film based valving technique was used for flow actuation and integration of multiple assays on the centrifugal cartridge. This new approach forms the basis of a cost efficient, USB-controlled water quality monitoring system. Technically, this integrated system consists of two components; a microfluidic disc (figure 1.A), the disc-holder fabricated and assembled from a 3D-printed casing, with electronic components housed in device. The 5-layered microfluidic disc consists of five reservoirs (figure 1.B), each with a separate venti-lation, aligned radially with inter-connected microchannels. A competitive immunoassay format is utilised to detect free toxin (figure 1.C). Sensitivity, reproducibility and ease-of-use are key features of this monitoring device. The ‘top-down’ optical detection system has been modified for improved detection sensitivity, as well as the elimination of external noise

A centrifugal lab-on-a-disc device for the in situ determination of dissolved reactive phosphate in water.

Phosphorus (P) is an important nutrient to monitor in natural waters as it is a growth limiting nutrient. When levels of phosphorus are elevated, excessive growth of algae occurs. This can lead to hypoxic or anoxic waters, potential release of harmful toxins and it impacts negatively on the ecosystem. Phosphorus measurement in water involves the collection of grab samples, transport and storage of samples, and analysis using expensive analytical instrumentation. This is costly, time and labour intensive and is carried out infrequently as a result. In this work, P is measured as soluble reactive phosphate (SRP), to give an indication of P levels in fresh water. A device for in situ analysis of SRP was fabricated. This device consists of a centrifugal microfluidic lab-on-a-disc platform, with a housing unit. The disc operates by mixing the sample with ascorbic acid method reagents using centrifugal force. The coloured product is presented to an optical detection system consisting of a laser and photodiode. The limit of detection has been optimised by modification of the optical path length. The housing unit is a 3D printed portable box with a built in motor for disc rotation. This box also houses the optical detection system which consists of a laser and photodiode. The box facilitates the alignment of the detection system with the optical pathway of the disc for absorbance measurements in an environment free from ambient light. This device allows for rapid analysis times, compactness, ease of use, low cost analyses and low reagent consumption. Keywords: Phosphate, microfluidics, lab-on-a-disc, optical senso