Abstract-A novel portable fluorometer combining the attributes of a smartphone with an easy-fit, simple and compact sample chamber fabricated using 3D printing has been developed for pH measurements of environmental water in the field. A colour filter attached over the camera white light LED selects an excitation band centred around λ ~ 450 nm with a 3 dB bandwidth, ∆λ ~ 21 nm. An application-specific, temperature stable chemosensor based on the 4-aminonaphthalimide fluorophore was synthesized to absorb at this wavelength whilst emitting in the green region of visible spectra. The green emission is readily detected using the smartphone camera and a simple RGB Android application. Suppression of the green emission increases with increasing pH enabling a straightforward pH sensor. The system was calibrated against a commercial spectrofluorometer and pH measurements were taken at various locations around Sydney. The results were then compared directly with those obtained using conventional electrode based measurements. The data can be stored in the phone's available memory or transmitted by phone back to base for further realtime analysis.

A structured optical fibre is drawn from a 3D-printed structured preform. Preforms containing a single ring of holes around the core are fabricated using filament made from a modified butadiene polymer. More broadly, 3D printers capable of processing soft glasses, silica and other materials are likely to come on line in the not-so-distant future. 3D printing of optical preforms signals a new milestone in optical fibre manufacture.In recent years, there has been an explosion of interest in 3D printing technologies and there is now a vast range of 3D printing methods that are finding new applications every day in a whole host of areas from science and engineering to medicine and the arts [1]. They are set to revolutionise manufacturing. Fused deposition modelling (FDM) is one of the most commonly used techniques, being the first and simplest demonstration of 3D printing in the late 1980s [2]. It is especially suited for instrument prototype casings such as those required for novel smartphone spectrometers [3]. In FDM, a polymer is fed through a heated nozzle which melts the polymer -essentially a fancy thermal glue gun using a finite extrusion nozzle with programmable xyz positioning capability. Optical polymerisation methods using both light emitting diodes (LEDs) and lasers offer higher resolution and are increasingly popular; however, they do not have the same material range given the specific absorption and monomer polymerization requirements. Selective laser sintering (SLS) is another popular technique where a high power laser is utilised to fuse not only plastic, but glass, metal or ceramic particles or powders into 3D objects [4]. A 3D profile is achieved by scanning the laser on the horizontal plane layer-by-layer, lowering the printing bed between each layer. All these methods have their particular rate limiting steps determined by the consolidation process details and the need for full xyz scanning. More recently, holographic imaging using projectors promises significantly accelerated production of the 3D printed object by removing the requirement for xy scanning [5]. FDM, SLS and other related variants are experiencing tremendous growth world-wide, particularly for rapid prototyping and manufacturing. 3D printing is also being applied to cellular assembly processing of biomedical interest [6]. 3D printing technologies are reaching most fields, including more recently photonics. For example, a company called Luxexcel is already producing high transparency Fresnel lenses by printing with polymethylmethacrylate (PMMA) filament [7]. Most interesting, is recent work demonstrating directprint short, solid plastic fibre [8] and "light pipes" [9] using transparent polymers, the first 3D printed waveguides.Here, we explore harnessing 3D printing for optical fibre fabrication. We see it as revolutionising the manufacture of all optical fibre fabrication, including glass optical fibres as 3D glass printing comes on line [10,11]. Whilst there is debate as to the merits of the technology for conventional step-index...

A combined "dual" absorption and fluorescence smartphone spectrometer is demonstrated. The optical sources used in the system are the white flash LED of the smartphone and an orthogonally positioned and interchangeable UV (λ_ex=370  nm) and blue (λ_ex=450  nm) LED. The dispersive element is a low-cost, nano-imprinted diffraction grating coated with Au. Detection over a 300 nm span with 0.42 nm/pixel resolution was carried out with the camera CMOS chip. By integrating the blue and UV excitation sources into the white LED circuitry, the entire system is self-contained within a 3D printed case and powered from the smartphone battery; the design can be scaled to add further excitation sources. Using a customized app, acquisition of absorption and fluorescence spectra are demonstrated using a blue-absorbing and green-emitting pH-sensitive amino-naphthalimide-based fluorescent probe and a UV-absorbing and blue-emitting Zn²⁺-sensitive fluoro-ionophore.

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Environmental contextArsenic contamination of groundwater is a major environmental problem in many areas of the world. In south-east Asia, iron-rich reducing groundwater mixes with oxidising river water in hyporheic zones, precipitating iron oxides. These oxides can act as a natural reactive barrier capable of accumulating elevated solid-phase concentrations of arsenic. AbstractShallow, anoxic aquifers within the Ganges–Brahmaputra–Meghna Delta (GBMD) commonly contain elevated concentrations of arsenic (As), iron (Fe) and manganese (Mn). Highly enriched solid-phase concentrations of these elements have been observed within sediments lining the banks of the Meghna River. This zone has been described as a Natural Reactive Barrier (NRB). The impact of hydrological processes on NRB formation, such as transient river levels, which drive mixing between rivers and aquifers, is poorly understood. We evaluated the impact of groundwater flow dynamics on hydrobiogeochemical processes that led to the formation of an Fe- and Mn-rich NRB containing enriched As, within a riverbank aquifer along the Meghna River. The NRB dimensions were mapped using four complementary elemental analysis methods on sediment cores: X-ray fluorescence (XRF), aqua regia bulk extraction, and HCl and sodium phosphate leaching. It extended from 1.2 to 2.4 m in depth up to 15 m from the river’s edge. The accumulated As was advected to the NRB from offsite and released locally in response to mixing with aged river water. Nearly all of the As was subsequently deposited within the NRB before discharging to the Meghna. Significant FeII release to the aqueous phase was observed within the NRB. This indicates the NRB is a dynamic zone defined by the interplay between oxidative and reductive processes, causing the NRB to grow and recede in response to rapid and seasonal hydrologic processes. This implies that natural and artificially induced changes in river stages and groundwater-tables will impact where As accumulates and is released to aquifers.

A smartphone fluorimeter capable of time-based fluorescence intensity measurements at various temperatures is reported. Excitation is provided by an integrated UV LED (λ = 370 nm) and detection obtained using the in-built CMOS camera. A Peltier is integrated to allow measurements of the intensity over T = 10 to 40 °C. All components are controlled using a smartphone battery powered Arduino microcontroller and a customised Android application that allows sequential fluorescence imaging and quantification every δt = 4 seconds. The temperature dependence of fluorescence intensity for four emitters (rhodamine B, rhodamine 6G, 5,10,15,20-tetraphenylporphyrin and 6-(1,4,8,11-tetraazacyclotetradecane)2-ethyl-naphthalimide) are characterised. The normalised fluorescence intensity over time of the latter chemosensor dye complex in the presence of Zn is observed to accelerate with an increasing rate constant, k = 1.94 min at T = 15 °C and k = 3.64 min at T = 30 °C, approaching a factor of ∼2 with only a change in temperature of ΔT = 15 °C. Thermally tuning these twist and bend associated rates to optimise sensor approaches and device applications is proposed.

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The temperature distribution within extrusion nozzles of three low cost desktop 3D printers are characterised using fibre Bragg gratings (FBGs) to assess their compatibility as micro-furnaces for topical fibre and taper production. These profiles show remarkably consistent distributions suitable for direct drawing of optical fibre. As proof of principle, coreless optical fibres (ϕ = 30 µm) made from fluorinated acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate glycol (PETG) are drawn. Cut-back measurements demonstrate propagation transmission losses as low as α = 0.26 dB/cm, comparable with standard optical fibre losses with some room for improvement. This work points towards direct optical fibre manufacture of any material from 3D printers.