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Giardia lamblia is a waterborne parasite that causes an intestinal infection, known as giardiasis, and it is found not only in countries with inadequate sanitation and unsafe water but also streams and lakes of developed countries. Simple, sensitive, and rapid detection of this pathogen is important for monitoring of drinking water. Here we present a cost-effective and field portable mobile-phone based fluorescence microscopy platform designed for automated detection of Giardia lamblia cysts in large volume water samples (i.e., 10 ml) to be used in low-resource field settings. This fluorescence microscope is integrated with a disposable water-sampling cassette, which is based on a flow-through porous polycarbonate membrane and provides a wide surface area for fluorescence imaging and enumeration of the captured Giardia cysts on the membrane. Water sample of interest, containing fluorescently labeled Giardia cysts, is introduced into the absorbent pads that are in contact with the membrane in the cassette by capillary action, which eliminates the need for electrically driven flow for sample processing. Our fluorescence microscope weighs ~170 grams in total and has all the components of a regular microscope, capable of detecting individual fluorescently labeled cysts under light-emitting-diode (LED) based excitation. Including all the sample preparation, labeling and imaging steps, the entire measurement takes less than one hour for a sample volume of 10 ml. This mobile phone based compact and cost-effective fluorescent imaging platform together with its machine learning based cyst counting interface is easy to use and can even work in resource limited and field settings for spatio-temporal monitoring of water quality.

Spatial Light Modulators (SLMs) have been successfully used for beam sculpting in the area of optical manipulation, however in some applications their associated pixelation, slow switching speeds, and incident power limitations can be undesirable. An alternative device that overcomes these problems is the Tunable Acoustic Gradient index (TAG) lens. This device uses acoustically induced density and refractive index variations within a fluid to spatially phase modulate a transmitted laser beam. The acoustic waves within the fluid are generated via a piezoelectric transducer. When driven with a frequency-modulated signal, arbitrary optical phase modulation patterns can be generated at regular time intervals. The resulting sculpted beam is best observed using a pulsed laser synchronized to the frequency-modulated signal of the TAG lens. As this device is purely analog, there is no pixelation in the phase modulation pattern. Also, because the only major requirement on the fluid is that it be transparent, it is possible to select fluids with high damage thresholds and high viscosities. High damage thresholds allow the TAG lens to be used in high power applications that would be unsuitable for an SLM. High viscosities provide fast damping of transient density variations and increase switching speeds between patterns. Discussion here will be limited to axially symmetric beam sculpting, however the results can be generalized to asymmetric cases.

The Tunable Acoustic Gradient Index of Refraction (TAG) lens is shown to be an alternative method of generating Bessel beam for optical manipulation. The TAG lens exhibits a combination of tunability, optical throughput, and fast switching speed, overcoming many limitations linked with conventional Bessel beam techniques. A refractive fluid is contained within a circular piezoelectric that is driven with an AC signal to establish a periodic index of refraction in the liquid. Simple changes in amplitude or frequency of the driving signal allows for the rapid modification to the transmitted pattern. The switching speed is characterized by the time to reach a steady state pattern, which is shown to depend primarily on the viscosity of the filling liquid. Times between 300 and 2000 μs are obtained corresponding to fluids with viscosity of 640 cs and 0.65 cs respectively.