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  • Journal article
    Alam F, Elsherif M, AlQattan B, Ali M, Ahmed IMG, Salih A, Antonysamy DS, Yetisen AK, Park S, Butt Het al., 2020,

    Prospects for additive manufacturing in contact lens devices

    , Advanced Engineering Materials, Vol: 23, ISSN: 1438-1656

    Additive manufacturing (3D printing) has the ability to architect structures at microscale, giving rise to the development of functional contact lenses (CLs) with inbuilt sensing capabilities. 3D printing technology enables fabrication of CLs without surface geometry restrictions. Spherical, nonspherical, symmetric, and asymmetric lenses can be manufactured in an integrated production process. Advantages of 3D printing over conventional techniques include fast and easy production, one-step manufacturing, and no post processing such as grinding or polishing. In addition, and most significantly, 3D printing can create chambers within the wall of the lenses by taking the advantage of computer-aided modeling and layer-by-layer deposition of the materials. These inbuilt chambers can be used for loading drugs and sensing elements. The computer-aided design modeling can allow for manufacturing of patient-specific CLs. This article focuses on the 3D-printing approaches and the challenges faced in fabricating CLs. 3D-printing technology as a technique for manufacturing of CLs is discussed, in addition to the manufacturing challenges and the possible solutions to overcome the obstacles.

  • Journal article
    Jiang N, Yetisen AK, Linhart N, Flisikowski K, Dong J, Dong X, Butt H, Jakobi M, Schnieke A, Koch AWet al., 2020,

    Fluorescent dermal tattoo biosensors for electrolyte analysis

    , Sensors and Actuators B: Chemical: international journal devoted to research and development of physical and chemical transducers, Vol: 320, ISSN: 0925-4005

    Dehydration, the abnormal depletion of body fluid, has been considered to greatly affect metabolic activities that may cause electrolyte disorder. However, current diagnostic approaches often fail to provide rapid and accurate electrolyte measurements in point-of-care settings. Here, fluorescent dermal tattoo sensors were developed to monitor electrolytes (e.g. H+, Na+, and K+ ions) in dermal interstitial fluids by using a customizable tattoo sensing platform. This platform consists of multiplexed fluorescent sensors including seminaphtorhodafluor, fluorescent diaza-15-crown-5 ether, and fluorescent diaza-18-crown-6 ether tattooed in the skin tissue. A portable optical readout device comprised of a smartphone, excitation light sources, and optical bandpass filters is developed to measure the fluorescence emission intensity of the tattoo sensors. The smartphone readout application features a user interface and a compensation algorithm to estimate electrolyte concentrations. Ex vivo studies in porcine skin tissues show that the tattooed sensors could provide quantitative results of electrolytes in dermis. These dermal sensors detect pH value, Na+ and K+ ions in the ranges of 6.6–7.6, 100−175 mmol L−1, and 2.0–6.0 mmol L−1. The detected emission intensities are converted to the concentration values of electrolytes and display in the smartphone diagnostic report. The dermal tattoo sensor may enable continual assessment of hydration status in point-of-care settings.

  • Journal article
    Dong J, Yetisen AK, Dong X, Poller F, Jakobi M, Liu Z, Bloise FS, Koch AWet al., 2020,

    Low-pass filtering compensation in common-path digital holographic microscopy

    , Applied Physics Letters, Vol: 117, ISSN: 0003-6951

    A low-pass filtering compensation (LPFC) method is proposed to compensate for phase aberrations in point diffraction-based common-path digital holographic microscopy. This method estimates the phase aberration from the object hologram by Fourier transform and low-pass spatial filtering. The estimated phase aberration is subtracted from the object phase image to achieve single-hologram phase compensation. The accuracy and capability of LPFC for phase compensation were demonstrated by experiments on a Ronchi grating and a human blood smear. LPFC provides phase compensation for both smooth objects and objects containing abrupt edges, in the special case of a system with relatively high-frequency objects and low-frequency slight phase aberrations. LPFC operates without the need for fitting procedures, iterative steps, or prior knowledge of the optical parameters, which substantially simplifies the process of phase compensation in quantitative phase imaging.Digital holographic microscopy (DHM) has been developed for a wide range of applications in the examination of cell pathophysiology,1,2 semiconductors,3 and 2D materials.4 Common-path DHM combines common-path geometry and off-axis holography, and hence, it provides subnanometer level optical phase delay (OPD) imaging with high temporal stability and the acquisition speed is limited only by the detector.5–8 Point diffraction-based common-path DHM uses a spatial filter to generate holograms with uniform reference fields, resulting in a compact system with a full field of view (FOV).9–13 In these setups, the zeroth-order beam is low-pass filtered by a pinhole in the Fourier plane of the spatial filtering lens, which is generally assumed to be a uniform field at the surface of the image sensor.11,13 However, due to the use of a microscope objective (MO) and the complex spatial filter, or a non-optimal imaging system, the zeroth-order beam can be distorted, which introduces phase aberrations to the original off

  • Conference paper
    Vasquez ESL, Yetisen AK, Vega K, 2020,


    , UbiComp/ISWC '20: 2020 ACM International Joint Conference on Pervasive and Ubiquitous Computing and 2020 ACM International Symposium on Wearable Computers, Publisher: ACM
  • Journal article
    Moreddu R, Wolffsohn JS, Vigolo D, Yetisen AKet al., 2020,

    Laser-inscribed contact lens sensors for the detection of analytes in the tear fluid

    , Sensors and actuators B: Chemical, Vol: 317, ISSN: 0925-4005

    Tears exhibit compositional variations as a response to ocular and systemic metabolic conditions, and they can therefore be used for the assessment of physiological health. Here, microfluidic contact lenses were developed as wearable platforms for in situ tear pH, glucose, protein, and nitrite ions sensing. The microfluidic system was inscribed in commercial contact lenses by CO2 laser ablation. The microchannel consisted on a central ring with four branches, and biosensors were embedded within microcavities located at the branches ends. The device was tested with artificial tears and colorimetric readouts were performed using a smartphone-MATLAB algorithm based on the nearest neighbor model. Sensors responded within a time range of 15 s, and yielded sensitivities of 12.23 nm/pH unit, 1.4 nm/mmol L−1 of glucose, 0.49 nm/g L−1 of proteins, and 0.03 nm/μmol L−1 of nitrites. Contact lens sensing platforms may provide on-eye tears screening with applications in the monitoring of the ocular health both in clinics and at point-of-care settings.

  • Journal article
    Ali M, Elsherif M, Salih AE, Ul-Hamid A, Hussein MA, Park S, Yetisen AK, Butt Het al., 2020,

    Surface modification and cytotoxicity of Mg-based bio-alloys: An overview of recent advances

    , Journal of Alloys and Compounds, Vol: 825, ISSN: 0925-8388

    The use of magnesium and its alloys for bone implants, cardiovascular stents, and wound closing devices have received considerable attention recently, however, their rapid degradation remains a major concern. Mg-based alloys degrade in the body prior to the completion of their specified healing period. Various biocompatible coatings have been used to overcome this shortcoming and to improve the surface properties such as hardness, corrosion resistance, and biocompatibility. The biocompatible materials used include calcium phosphate (Ca–P), hydroxyapatite (HA), octa calcium phosphate (Octa-Ca-P), metals (Zr, N, Hf, Nd, Zn, Cr, O, Ti), metal oxides (Al2O3, ZrO2, Cr2O3, SiO2, TiO2, Ta2O5, MgO), fluorides, and biopolymers. This paper reviews the surface treatment techniques utilized for Mg and Mg alloys. Additionally, related problems and possible solutions for Mg-based alloys with cytotoxicity are discussed.

  • Journal article
    Hendi A, Hassan MU, Elsherif M, Alqattan B, Park S, Yetisen AK, Butt Het al., 2020,

    Healthcare applications of pH-sensitive hydrogels based devices: a review

    , International Journal of Nanomedicine, Vol: 2020, Pages: 3887-3901, ISSN: 1176-9114

    pH-sensitive hydrogels have developed greatly over the past few years. This has been possible due to the synthesis of new hydrogel systems with increased sensitivity - the sensitivity of up to 10-5 pH units have already been established. Recently, pH-sensitive hydrogels have shown to be very useful for biomedical applications, such as targeted cancer treatment and treatment of skin lesions. Prolonged drug release has been made available through the use of such hydrogels. The synthesis of pH-sensitive hydrogels is also quick and cost-effective. This review presents a background on the properties of pH-sensitive hydrogels and discusses some of the hydrogels with different sensitivity ranges and their possible applications. A range of synthesis processes has also been briefly introduced along with the fabrication of different structures such as microcantilevers and contact lenses.

  • Journal article
    Salih AE, Elsherif M, Ali M, Vahdati N, Yetisen AK, Butt Het al., 2020,

    Ophthalmic wearable devices for color blindness management

    , Advanced Materials Technologies, Vol: 5, ISSN: 2365-709X

    Color vision deficiency (CVD) or color blindness is an ocular disorder that hinders the patients from distinguishing shades of certain colors. Color blind patients are often not considered for critical occupations (e.g., military, police) and cannot differentiate colors in public places or media (i.e., watching TV). The most common form of color blindness is red-green, which is a result of either a missing or defective red or green photoreceptor cone. Since no cure for this disorder exists, sufferers opt for methods to enhance their color perception. The products and methods that have been developed to aid CVD patients are discussed. These technologies include contemporary work on gene therapy, tinted glasses, lenses, optoelectronic glasses, and advanced features developed on smartphones and computers. Among these wearables, tinted glasses, developed by companies such as Enchroma, are the most widely used by CVD patients.

  • Journal article
    Dong X, Yetisen AK, Tian H, Gueler I, Stier A, Li Z, Koehler MH, Dong J, Jakobi M, Finley JJ, Koch AWet al., 2020,

    Line-scan hyperspectral imaging microscopy with linear unmixing for automated two-dimensional crystals identification

    , ACS Photonics, Vol: 7, Pages: 1216-1225, ISSN: 2330-4022

    Two-dimensional (2D) materials exhibit unique optical properties when controlled to atomic thickness, and show large potential for applications in optoelectronics, photodetectors, and tunable excitonic devices. Current characterization techniques, including conventional optical microscopy, atomic force microscopy (AFM), and Raman spectroscopy are time-consuming and labor-intensive for studying large-scale samples. To realize the rapid identification of monolayer and few-layer crystals in the “haystack” of hundreds of flakes appearing in the exfoliation process, line-scan hyperspectral imaging microscopy combined with linear unmixing was developed to identify 2D molybdenum disulfide (MoS2) and hexagonal boron nitride (hBN) samples. A complete hyperspectral measurement and analysis, including single-band analysis, pixel-level spectral analysis and image classification was performed on MoS2 and hBN flakes with mono- and few-layer thickness. The characteristic spectra were extracted and analyzed via linear unmixing calculations to reconstruct the distribution images. The abundance maps showed the spatial distribution of these flakes with flake positions output, realizing an automatic identification of target flakes. This work shows a rapid and robust method for the determination of abundance maps of 2D flakes distributed over macroscopic areas.

  • Journal article
    Sharma N, Bergholt MS, Moreddu R, Yetisen AKet al., 2020,

    Clinician engineers – re-injecting the thinking into medicine

    , The Asia Pacific Scholar, Vol: 5, Pages: 48-50, ISSN: 2424-9335

    INTRODUCTIONMedicine historically relied on astute history and examination skills. As technology was lacking, ward rounds focused on debate and discussion of diagnoses and possible differential diagnoses based on the history and physical examination. The technology movement into healthcare was never truly predicted. With its occurrence, came the ability to scan a patient from top to toe via computed tomography and magnetic resonance imaging. Technology now serves as our main diagnostic tool (Patel, 2013)

  • Journal article
    Dong X, Yetisen AK, Tian H, Dong J, Koehler MH, Jakobi M, Koch AWet al., 2020,

    Analyses of hyperspectral imaging microscopy data sets of semiconducting 2D materials

    , Applied Physics Express, Vol: 13, ISSN: 1882-0778

    The unique optical properties of two-dimensional (2D) materials are largely dependent on the number of atomic layers. Hyperspectral imaging microscopy shows large potential for rapid and accurate thickness mapping. To process the acquired hyperspectral data set and to deal with pixel-level spectra remain a challenge for further application. In this work, two quantitative classification strategies including linear unmixing and spectral peak mapping were conducted to characterize a multilayer semiconducting MoS2 flake with nanoscale thickness variations. The comparative study paves the way to identify 2D semiconducting materials with random layer numbers (monolayer, bilayer, and few-layer) in both laboratory and industry.

  • Journal article
    Dong J, Wang S, Yetisen AK, Dong X, Poeller F, Ong N, Jakobi M, Liu Z, Salazar Bloise F, Koch AWet al., 2020,

    Shear-unlimited common-path speckle interferometer

    , Optics Letters, Vol: 45, Pages: 1305-1308, ISSN: 0146-9592

    A single-aperture common-path speckle interferometer with an unlimited shear amount is developed. This unlimited shear amount is introduced when a Wollaston prism is placed near the Fourier plane of a common-path interferometer, which is built by using a quasi-4𝑓 imaging system. The fundamentals of the shear amount and the spatial carrier frequency generation are analyzed mathematically, and the theoretical predictions are validated by a static experiment. Mode-I fracture experiments through the three-point bending are conducted to prove the feasibility and the capability of this method in full-field strain measurement with various shear amounts. A remarkable feature of this setup is that no tilt is required between the optical components to produce the unlimited shear amount in off-axis holography.

  • Journal article
    Yetisen AK, Jiang N, Castaneda Gonzalez CM, Erenoglu ZI, Dong J, Dong X, Stößer S, Brischwein M, Butt H, Cordeiro MF, Jakobi M, Hayden O, Koch AWet al., 2020,

    Scleral lens sensor for ocular electrolyte analysis

    , Advanced Materials, Vol: 32, ISSN: 0935-9648

    The quantitative analysis of tear analytes in point-of-care settings can enable early diagnosis of ocular diseases. Here, a fluorescent scleral lens sensor is developed to quantitatively measure physiological levels of pH, Na+ , K+ , Ca2+ , Mg2+ , and Zn2+ ions. Benzenedicarboxylic acid, a pH probe, displays a sensitivity of 0.12 pH units within pH 7.0-8.0. Crown ether derivatives exhibit selectivity to Na+ and K+ ions within detection ranges of 0-100 and 0-50 mmol L-1 , and selectivities of 15.6 and 8.1 mmol L-1 , respectively. A 1,2 bis(o-aminophenoxy)ethane-N,N,-N',N'-tetraacetic-acid-based probe allows Ca2+ ion sensing with 0.02-0.05 mmol L-1 sensitivity within 0.50-1.25 mmol L-1 detection range. 5-Oxazolecarboxylic acid senses Mg2+ ions, exhibiting a sensitivity of 0.10-0.44 mmol L-1 within the range of 0.5-0.8 mmol L-1 . The N-(2-methoxyphenyl)iminodiacetate Zn2+ ion sensor has a sensitivity of 1 µmol L-1 within the range of 10-20 µmol L-1 . The fluorescent sensors are subsequently multiplexed in the concavities of an engraved scleral lens. A handheld ophthalmic readout device comprising light-emitting diodes (LEDs) and bandpass filters is fabricated to excite as well as read the scleral sensor. A smartphone camera application and an user interface are developed to deliver quantitative measurements with data deconvolution. The ophthalmic system enables the assessment of dry eye severity stages and the differentiation of its subtypes.

  • Journal article
    Jiang N, Muck JE, Yetisen AK, 2020,

    The regulation of wearable medical devices

    , Trends in Biotechnology, Vol: 38, Pages: 129-133, ISSN: 0167-7799

    This article provides a guideline for the design, manufacture, regulatory approval, and post-market surveillance (PMS) of wearable medical devices (WMDs). The integration of regulatory considerations can accelerate wearable device (WD) development from laboratory to market while mitigating device failure risks. The implementation of stringent clinical evaluations will transcend WDs beyond consumer products.

  • Journal article
    Kurz W, Yetisen AK, Kaito MV, Fuchter MJ, Jakobi M, Elsner M, Koch AWet al., 2020,

    UV-sensitive wearable devices for colorimetric monitoring of UV exposure

    , Advanced Optical Materials, Vol: 8, ISSN: 2195-1071

    The extensive exposure of the human epidermis to solar radiation creates a health risk that results in skin cancer. Commercial sunscreens offer sufficient protection from ultraviolet (UV) radiation; however, the ability to determine UV exposure limits can provide informed decisions about the dose of sunscreen required and the frequency of re-application. Here, a wide range of wearable devices that colorimetrically report on UV exposure are developed. Under UV radiation, UV-sensitive dyes change their color from 280 to 400 nm in the visible spectrum. By correlating the current color value and the UV dose, the amount of sun exposure is determined with an accuracy of 95%. A smartphone camera algorithm is coded to automatically perform the color analysis of these dyes. The UV-sensitive dyes are incorporated in wearable devices, skin patches, textiles, contact lenses, and tattoo inks. The developed wearable devices will ensure monitoring UV radiation to rationally manage the user's behavior in order to prevent harmful sun exposure.

  • Journal article
    Soussi S, Bergholt MS, Yetisen AK, Sharma Net al., 2020,

    Clinician engineers: The future of medical education

    , Medical Teacher, Vol: 42, Pages: 478-478, ISSN: 0142-159X
  • Journal article
    Riaz RS, Elsherif M, Moreddu R, Rashid I, Hassan MU, Yetisen AK, Butt Het al., 2019,

    Anthocyanin-functionalized contact lens sensors for ocular pH monitoring

    , ACS Omega, Vol: 4, Pages: 21792-21798, ISSN: 2470-1343

    Anthocyanins are bioactive compounds naturally found in a variety of leaves, fruits, and vegetables. Anthocyanin pigments undergo a modification in their chemical structure when exposed to different concentrations of hydrogen ions, and they were extensively studied to be used as active elements in biocompatible pH sensors. The ocular pH is a significant parameter to assess the ocular physiology in cases of postocular surgery, keratoconjunctivitis, and ocular rosacea. Contact lenses have the potential to be used as medical diagnostic devices for in situ continuous monitoring of the ocular physiology. Here, anthocyanin-functionalized contact lenses were developed as wearable sensors to monitor the ocular pH. Anthocyanin pigments were extracted from Brassica oleracea and used to functionalize the polymeric matrices of commercial soft contact lenses by soaking and drop-casting processes. Contact lenses responded to the physiological ocular pH of 6.5, 7.0, and 7.5, exhibiting a systematic color shift from pink (pH 6.5) to purple (pH 7.0) and blue (pH 7.5). The functionalization of contact lens sensors was evaluated as a function of the dye concentration. Quantitative values were obtained by comparing the RGB triplets of the colors obtained with the naturally extracted dye and with delphinidin chloride dye in 0.0 to 1.5 mmol L–1 aqueous solution. The functionalization of contact lenses was studied as a function of the soaking time, resulting in best results when soaking for 24 h. The dye leakage from the contact lenses in deionized water was evaluated, and a negligible leakage after 18 h was observed. Poly-2-hydroxy ethylmethacrylate contact lenses were fabricated and cross-linked with anthocyanin dye, resulting in a slight color shift upon pH changes from 6.5 to 7.4. Contact lens pH sensors may be used to continuously monitor the ocular pH at point-of-care settings.

  • Journal article
    Dong X, Dong J, Yetisen AK, Koehler MH, Wang S, Jakobi M, Koch AWet al., 2019,

    Characterization and layer thickness mapping of two-dimensional MoS2 flakes via hyperspectral line-scanning microscopy

    , Applied Physics Express, Vol: 12, ISSN: 1882-0778

    A micro-reflectance imaging system based on hyperspectral line-scanning microscope is developed for surface characterization and thickness mapping of two-dimensional MoS2. The hyperspectral datacube of region of interest (120 × 200 μm2) is obtained with microscale spatial resolution. Single-band quantitative analysis shows distributions of different thicknesses with wavelength variations. The excitonic peak with position around 655 nm is measured by differential reflectance analysis. Peak position mapping is employed for imaging MoS2 flakes with specific thickness and reconstructed images perform the same region of interest with high accuracy. The developed micro-reflectance imaging system has applications in laboratory analyses and industrial monitoring of 2D materials.

  • Journal article
    AlQattan B, Benton D, Yetisen AK, Butt Het al., 2019,

    Conformable Holographic Photonic Ink Sensors Based on Adhesive Tapes for Strain Measurements.

    , ACS Appl Mater Interfaces

    Buildings, bridges, and aircrafts are frequently exposed to fluctuation loads, which could start with a fine crack that instantly leads to unpredictable structure failures. The stationary strain sensors can be utilized, but they are costly and only detect limited deformation forms and sizes. Here, we fabricated photonic strain sensors on adhesive tapes, which can provide real-time monitoring of irregular surfaces. Holographic interference patterning was used to produce nonlinear curved nanostructures of one dimensional (1D) (900 nm × 880 nm) and two dimensional (2D) from a black dye film on a robust uniform adhesive layer and heat resistance tape. The patterned structure of the black dye was stable in broad pH environments. Diffracted light from the curved nanostructure detected the signal during structural damage, a shift or material tear of 5 με at less than 1.3 N cm-2. Additionally, the 2D nanostructure detected a surface change from x or y axis. Tilting the 1D structure within a range of 0.3° to 14.2° provided visible wavelength changes under broadband light to reveal early deflection signs. The curved nanopatterns could be also used for transferable holographic symbol design. Photonic nanopatterns on an adhesive tape could be used as a rapid response, conformable, lightweight, and low-cost dynamic strain sensor.

  • Journal article
    Moreddu R, Vigolo D, Yetisen AK, 2019,

    Contact Lens Technology: From Fundamentals to Applications.

    , Adv Healthc Mater, Vol: 8, Pages: e1900368-e1900368

    Contact lenses are ocular prosthetic devices used by over 150 million people worldwide. Primary applications of contact lenses include vision correction, therapeutics, and cosmetics. Contact lens materials have significantly evolved over time to minimize adverse effects associated with contact lens wearing, to maintain a regular corneal metabolism, and to preserve tear film stability. This article encompasses contact lens technology, including materials, chemical and physical properties, manufacturing processes, microbial contamination, and ocular complications. The function and the composition of the tear fluid are discussed to assess its potential as a diagnostic media. The regulatory standards of contact lens devices with regard to biocompatibility and contact lens market are presented. Future prospects in contact lens technology are evaluated, with particular interest given to theranostic applications for in situ continuous monitoring the ocular physiology.

  • Journal article
    Yetisen AK, Moreddu R, Seifi S, Jiang N, Vega K, Dong X, Dong J, Butt H, Jakobi M, Elsner M, Koch AWet al., 2019,

    Dermal tattoo biosensors for colorimetric metabolite detection.

    , Angewandte Chemie International Edition, Vol: 58, Pages: 10506-10513, ISSN: 1433-7851

    Tattooing is a ubiquitous body modification involving the injection of ink and/or dye pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed for measuring pH, glucose, and albumin concentrations. The dermal pH sensor was based on methyl red, bromothymol blue, and phenolphthalein, which responded to a pH range from 5.0 to 9.0. The dermal glucose sensor consisted of glucose oxidase, 3,3',5,5'-tetramethylbenzidine, and peroxidase that detected concentrations up to 50.0 mmol L-1 . The dermal albumin sensor consisted of 3',3'',5',5''-tetrachlorophenol-3,4,5,6-tetrabromosulfophthalein to measure concentrations up to 5.0 g L-1 . The sensors were multiplexed in ex vivo skin tissue and quantitative readouts were obtained using a smartphone camera. These sensors can be used to manage of acid-base homeostasis, diabetes, and liver failure in point-of-care settings.

  • Journal article
    Jiang N, Ahmed R, Damayantharan M, Unal B, Butt H, Yetisen AKet al., 2019,

    Lateral and Vertical Flow Assays for Point-of-Care Diagnostics

  • Journal article
    Elsherif M, Hassan MU, Yetisen AK, Butt Het al., 2019,

    Hydrogel optical fibers for continuous glucose monitoring

    , Biosensors and Bioelectronics, Vol: 137, Pages: 25-32, ISSN: 0956-5663

    Continuous glucose monitoring facilitates the stringent control of blood glucose concentration in diabetic and intensive care patients. Optical fibers have emerged as an attractive platform; however, their practical applications are hindered due to lack of biocompatible fiber materials, complex and non-practical readout approaches, slow response, and time-consuming fabrication processes. Here, we demonstrate the quantification of glucose by smartphone-integrated fiber optics that overcomes existing technical limitations. Simultaneously, a glucose-responsive hydrogel was imprinted with an asymmetric microlens array and was attached to a multimode silica fiber's tip during photopolymerization, and subsequent interrogated for glucose sensing under physiological conditions. A smartphone and an optical power meter were employed to record the output signals. The functionalized fiber showed a high sensitivity (2.6 μW mM−1), rapid response, and a high glucose selectivity in the physiological glucose range. In addition, the fiber attained the glucose complexation equilibrium within 15 min. The lactate interference was also examined and it was found minimal ∼0.1% in the physiological range. A biocompatible hydrogel made of polyethylene glycol diacrylate was utilized to fabricate a flexible hydrogel fiber to replace the silica fiber, and the fiber's tip was functionalized with the glucose-sensitive hydrogel during the ultraviolet light curing process. The biocompatible fiber was quickly fabricated by the molding, the readout approach was facile and practical, and the response to glucose was comparable to the functionalized silica fiber. The fabricated optical fiber sensors may have applications in wearable and implantable point-of-care and intensive-care continuous monitoring systems.

  • Journal article
    Elsherif M, Moreddu R, Hassan MU, Yetisen AK, Butt Het al., 2019,

    Real-time optical fiber sensors based on light diffusing microlens arrays

    , LAB ON A CHIP, Vol: 19, Pages: 2060-2070, ISSN: 1473-0197
  • Patent
    Yetisen AK, Choi M-G, Yun S-H, Lee B-I, Park JM, Kamrani Eet al., 2019,

    Stent Using Wireless Transmitted Power and External Operating Apparatus Thereof

    , 20190183665

    The present invention relates to a stent using wirelessly transmitted power, and to an external driving device thereof. To this end, a stent is provided with: a power receiving part wirelessly receiving power from the outside; a power storing part storing the power; a second communicating part receiving a control command from the outside; an electrical stimulation part generating electrical stimulation by using the power; a photosensitizer coated onto a stent; an LED illuminating the vicinity of the stent; and a second control part controlling the heat-generating stent on the basis of the control command.

  • Journal article
    Muck JE, Unal B, Butt H, Yetisen AKet al., 2019,

    Market and patent analyses of wearables in medicine

    , Trends in Biotechnology, Vol: 37, Pages: 563-566, ISSN: 0167-7799

    Wearable medical devices (WMDs) will advance point-of-care diagnostics and therapeutics. This article analyses the market and patents for wearable devices. Activity monitors have the largest market share, and the intellectual property landscape is dominated by electronics corporations. However, the majority of these patents have not been realized in commercial products.

  • Journal article
    Dong X, Yetisen AK, Köhler MH, Dong J, Wang S, Jakobi M, Zhang X, Koch AWet al., 2019,

    Microscale Spectroscopic Mapping of 2D Optical Materials

    , Advanced Optical Materials, Pages: 1900324-1900324, ISSN: 2195-1071
  • Journal article
    Moreddu R, Elsherif M, Butt H, Vigolo D, Yetisen AKet al., 2019,

    Contact lenses for continuous corneal temperature monitoring

    , RSC Advances, Vol: 9, Pages: 11433-11442, ISSN: 2046-2069

    Temperature variation is a ubiquitous medical sign to monitor ocular conditions including dry eye disease (DED), glaucoma, carotid artery stenosis, diabetic retinopathy, and vascular neuritis. The ability to measure OST in real time is desirable in point-of-care diagnostics. Here, we developed minimally invasive contact lens temperature sensors for continuous monitoring of the corneal temperature. The contact lens sensor consisted of a laser patterned commercial contact lens embedding temperature-sensitive Cholesteric Liquid Crystals (CLCs), which exhibited a fully reversible temperature-dependent color change in the visible spectrum. The contact lens allowed the corneal temperature to be mapped in four key areas, at distances of 0.0, 1.0, 3.0, and 5.0 mm from the pupil's edge. Liquid crystals exhibited a wavelength shift from 738 ± 4 nm to 474 ± 4 nm upon increasing the temperature from 29.0 °C to 40.0 °C, with a time responsivity of 490 ms and a negligible hysteresis. Readouts were performed using a smartphone, which output RGB triplets associated to temperature values. Contact lens sensors based on CLCs were fitted and tested on an ex vivo porcine eye and readouts were compared with infrared thermal measurements, resulting in an average difference of 0.3 °C.

  • Journal article
    Yetisen AK, Soylemezoglu B, Dong J, Montelongo Y, Butt H, Jakobi M, Koch AWet al., 2019,

    Capillary flow in microchannel circuitry of scleral lenses

    , RSC Advances: an international journal to further the chemical sciences, Vol: 9, Pages: 11186-11193, ISSN: 2046-2069

    Continuous monitoring of biomarkers in a quantitative manner at point-of-care settings can advance early diagnosis in medicine. Contact lenses offer a minimally-invasive platform to continuously detect biomarkers in tear fluid. Microfluidic components as lab-on-a-chip technology have the potential to transform contact lenses into fully-integrated multiplexed sensing devices. Here, simple and complex microchannels are created in scleral lenses that perform microfluidic operations via capillary action. The engraving of microchannels in scleral lenses were performed by laser micromilling, where a predictive computational model was developed to simulate the effect of laser power and exposure time on polymer behavior. Experimentally varying the CO2 laser power (1.2–3.6 W) and speed (38–100 mm s−1) allowed the micromilling of concave microchannels with groove depths of 10–240 μm and widths of 35–245 μm on polymetric substrates. The demonstrated laser micromilled circuitry in scleral lenses included linear channels, T/Y junctions, multiplexed arrays, mixers, and spiral channels, as well as serially organized multicomponent channels. Capillary forces acting in the microchannels allowed flowing rhodamine dye within the microfluidic components, which was visualized by optical microscopy in reflection and transmission modes simultaneously. The developed microfluidic components in scleral lenses may enable tear sampling, storage, analysis, and multiplexed detection capabilities for continuous monitoring applications.

  • Journal article
    Alqurashi T, Alnufaili M, Hassan MU, Aloufi S, Yetisen AK, Butt Het al., 2019,

    Laser Inscription of Microfluidic Devices for Biological Assays

    , ACS APPLIED MATERIALS & INTERFACES, Vol: 11, Pages: 12253-12260, ISSN: 1944-8244

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