Circulating Tumor Cells (CTCs) have emerged as an eligible biomarker for liquid biopsy. These cells are released in peripheral circulation at a very early stage from the tumor mass via metastatic or non-metastatic cascade. These cells provide a non-invasive method for cancer detection and monitoring. In this work, Gold Nanoparticle (GNP) decorated U-bent optical fiber was used as a sensor platform. For specific detection of cancer cells, an antibody for nucleolin protein which over-expresses on their surface was employed as a receptor. This Localized Surface Plasmon Resonance (LSPR) based biosensor poses salient features like high sensitivity, ease of fabrication, low cost, and handling. For sensor fabrication, optical fiber was decladded, bent in a U-shape, and cleaned. After GNPs, U-bent fiber was coated with cysteamine. The concentration and incubation time of cysteamine was optimized as they played a critical role in the sensitivity and specificity of the sensor. Next, the amine group of cysteamines was treated with glutaraldehyde to which the antibody was attached. Ethanolamine was used as a blocking agent and its incubation time was also optimized. The sensor was introduced to 104 MCF-7 cells and 105 WBCs in PBS buffer and the binding absorbance for 2 hours was monitored. The obtained absorbance for MCF-7 cells and WBCs was around 0.05±0.011 and 0.002±0.0015 O.D. respectively, which indicated a very high specificity of the sensor for cancer cells. The obtained results are promising and pave the way to develop a highly specific and affordable point-of-care device for cancer detection and monitoring.
Miniature lenses can transform commercial imaging systems, e.g., smartphones and webcams, into powerful, low-cost, handheld microscopes. To date, the reproducible fabrication of polymer lenses is still a challenge as they require controlled dispensing of viscous liquid. This paper reports a reproducible lens fabrication technique using liquid mold with programmable curvature and off-the-shelf materials. The lens curvature is controlled during fabrication by tuning the curvature of an interface of two immiscible liquids [polydimethylsiloxane (PDMS) and glycerol]. The curvature control is implemented using a visual feedback system, which includes a software-based guiding system to produce lenses of desired curvature. The technique allows PDMS lens fabrication of a wide range of sizes and focal lengths, within 20 min. The fabrication of two lens diameters: 1 and 5 mm with focal lengths ranging between 1.2 and 11 mm are demonstrated. The lens surface and bulk quality check performed using X-ray microtomography and atomic force microscopy reveal that the lenses are suitable for optical imaging. Furthermore, a smartphone microscope with ∼1.4-μm resolution is developed using a self-assembly of a single high power fabricated lens and microaperture. The lenses have various potential applications, e.g., optofluidics, diagnostics, forensics, and surveillance.
Aspherical optical lenses are known for high performance and aberration free imaging. They are increasingly in demand for developing simple and compact high quality optical systems. The conventional methods of production of aspherical lenses are complex and time-consuming. There is a need for a simple, inexpensive and robust method of fabrication of such lenses. Here, we present a novel, low cost and simple approach to fabricate aspherical lenses reproducibly. The two-step process involves 1) controlled wetting of a curved surface with a transparent, cross-linkable polymer by dipping, and 2) pulling the wetted curved surface from the polymer solution. The curvature of the lens is dependent on the area of wetting, speed of pulling and the curvature of the curved surface. The lenses are produced with less than 5% error, and hence, the approach is reproducible in comparison to the previously reported techniques. A smartphone microscope developed using one of the fabricated lenses is found to have a resolution of ~1.7 μm. In addition, we show an application of these lenses as a means to check for the authenticity of Indian currency notes by a common man. The micro-patterns on the currency note are imaged using the smartphone microscope in ambient light. Also, the lenses have potential applications in developing compact and portable high quality optical systems, such as, endoscopes and microscopes.
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