Smartphone Nanocolorimetry for On-Demand Lead Detection and Quantitation in Drinking Water.

Lead ions (Pb2+) contamination in drinking water, a major source of lead poisoning to the general population, is typically detected by bulky and costly laboratory analytical instrument. A mobile analytical device for rapid Pb2+ sensing is a growing demand. Herein, we report smartphone nanocolorimetry (SNC) as a new technique to detect and quantify dissolved Pb2+ in drinking water. Specifically, we have employed a single-step sedimentation approach by mixing a controlled quantity of chromate ion (CrO42-) to react with Pb2+ containing solutions to form highly insoluble lead chromate (PbCrO4) nanoparticles as vivid yellow precipitates. This is followed by microscopic color detection and intensity quantitation at nanoscale level using dark-field smartphone microscopy. The sum of the intensity of yellow pixels bears a highly reproducible relationship with Pb2+ concentration between 1.37 and 175 ppb in deionized water and 5-175 ppb in city tap water. In contrast to traditional colorimetric techniques analyzing bulk color changes, SNC achieves unparalleled sensitivity by combining nanocolorimetry with dark-field microscopy and mobilized the metal ions detection by integrating the detection into the smartphone microscope platform. SNC is rapid and low-cost and has the potential to enable individual citizens to examine Pb2+ content in drinking water on-demand in virtually any environmental setting.

Modeling the surface of fast-cured polymer droplet lenses for precision fabrication.

Optical lenses with diameter in the millimeter range have found important commercial use in smartphone cameras. Although these lenses are typically made by molding, recent demonstration of fast-cured polymer droplets by inkjet printing has gained interest for cost-effective smartphone microscopy. In this technique, the surface of a fast-cured polydimethylsiloxane droplet obtains dynamic equilibrium via the interplay of surface tension, gravity, thermalization, and a steep viscosity hike. The nature of surface formation involves multiple physical and chemical domains, which represent significant challenges in modeling with the Young-Laplace theory, assuming constant surface tension and viscosity. To overcome these challenges, we introduce the concept of effective surface tension, which allows fast-cured polymer droplets to be modeled as normal liquid droplets with constant viscosity.

Automated batch characterization of inkjet-printed elastomer lenses using a LEGO platform.

Small, self-adhesive, inkjet-printed elastomer lenses have enabled smartphone cameras to image and resolve microscopic objects. However, the performance of different lenses within a batch is affected by hard-to-control environmental variables. We present a cost-effective platform to perform automated batch characterization of 300 lens units simultaneously for quality inspection. The system was designed and configured with LEGO bricks, 3D printed parts, and a digital camera. The scheme presented here may become the basis of a high-throughput, in-line inspection tool for quality control purposes and can also be employed for optimization of the manufacturing process.

Open-source do-it-yourself multi-color fluorescence smartphone microscopy.

Fluorescence microscopy is an important technique for cellular and microbiological investigations. Translating this technique onto a smartphone can enable particularly powerful applications such as on-site analysis, on-demand monitoring, and point-of-care diagnostics. Current fluorescence smartphone microscope setups require precise illumination and imaging alignment which altogether limit its broad adoption. We report a multi-color fluorescence smartphone microscope with a single contact lens-like add-on lens and slide-launched total-internal-reflection guided illumination for three common tasks in investigative fluorescence microscopy: autofluorescence, fluorescent stains, and immunofluorescence. The open-source, simple and cost-effective design has the potential for do-it-yourself fluorescence smartphone microscopy.

Fabricating optical lenses by inkjet printing and heat-assisted in situ curing of polydimethylsiloxane for smartphone microscopy.

We present a highly repeatable, lithography-free and mold-free method for fabricating flexible optical lenses by in situ curing liquid polydimethylsiloxane droplets on a preheated smooth surface with an inkjet printing process. This method enables us to fabricate lenses with a focal length as short as 5.6 mm, which can be controlled by varying the droplet volume and the temperature of the preheated surface. Furthermore, the lens can be attached to a smartphone camera without any accessories and can produce high-resolution (1 µm) images for microscopy applications.

A low sample volume particle separation device with electrokinetic pumping based on circular travelling-wave electroosmosis.

Particle separation is a crucial step in sample preparation processes. The preparation of low volume samples is especially important for clinical diagnosis and chemical analysis. The advantages of microfluidic techniques have lead them to become potential candidates for particle separation. However, existing microfluidic devices require external pumping sources and extensive geometric patterns to attain high separation efficiency, which is disadvantageous when handling low volume samples. This paper presents a low sample volume particle separation microfluidic device with low voltage electrokinetic pumping based on circular travelling-wave electroosmosis (TWEO). Computational numerical software was utilized to simulate two electrokinetic mechanisms: circular TWEO and dielectrophoresis (DEP). The circular TWEO shear flow generates a velocity gradient in the radial direction which causes a shear stress-induced force to drag particles into the center region of the device. In contrast, the non-parallel electrodes induce negative DEP forces which push polystyrene beads towards the peripheral regions; the magnitude of the DEP forces are dependent on the sizes of the polystyrene beads. We used particles of various sizes to experimentally prove the concept of particle separation. Our experiments show that 15 µm beads are dragged into the center region due to the shear stress-induced force, and 1 µm beads move towards the outer region because of the large negative DEP force. The results show a separation purity of 94.4% and 80.0% for 15 µm and 1 µm beads respectively. We further demonstrated particle isolation from a sample of containing a small proportion of 6 µm beads mixed with 1 µm beads at a concentration ratio of 1 : 300. Therefore, the innovative device developed in this paper provides a promising solution to allow particle separation in sample volumes as low as 50 nL.