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  • 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, Vol: 320, ISSN: 0925-4005

    © 2020 Elsevier B.V. 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
    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
  • 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
  • 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, ISSN: 2365-709X
  • 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
  • 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
  • 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
  • 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, Pages: 1-17, 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
  • 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
  • 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
  • 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.

    , Angew Chem Int Ed Engl, Vol: 58, Pages: 10506-10513

    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

    , ADVANCED HEALTHCARE MATERIALS, Vol: 8, ISSN: 2192-2640
  • Journal article
    Elsherif M, Hassan MU, Yetisen AK, Butt Het al., 2019,

    Hydrogel optical fibers for continuous glucose monitoring

    , BIOSENSORS & BIOELECTRONICS, Vol: 137, Pages: 25-32, ISSN: 0956-5663
  • Journal article
    Soussi S, Bergholt MS, Yetisen AK, Sharma Net al., 2019,

    Clinician engineers: The future of medical education

    , MEDICAL TEACHER, ISSN: 0142-159X
  • 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
  • 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
  • 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, Vol: 9, Pages: 11186-11193, ISSN: 2046-2069
  • 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
  • Journal article
    Yin Y, Xiao G, Zhang K, Ying G, Xu H, De Melo BAG, Li S, Liu F, Yetisen AK, Jiang Net al., 2019,

    Tacrolimus- and Nerve Growth Factor-Treated Allografts for Neural Tissue Regeneration

    , ACS CHEMICAL NEUROSCIENCE, Vol: 10, Pages: 1411-1419, ISSN: 1948-7193
  • Journal article
    Coskun AF, Topkaya SN, Yetisen AK, Cetin AEet al., 2019,

    Portable Multiplex Optical Assays

    , ADVANCED OPTICAL MATERIALS, Vol: 7, ISSN: 2195-1071
  • Journal article
    Dong J, Wang S, Lu M, Jakobi M, Liu Z, Dong X, Poeller F, Bilgeri LM, Salazar Bloise F, Yetisen AK, Koch AWet al., 2019,

    Real-time dual-sensitive shearography for simultaneous in-plane and out-of-plane strain measurements

    , Optics Express, Vol: 27, Pages: 3276-3283, ISSN: 1094-4087

    A real-time, dual-sensitive shearography system using a single-wavelength laser was developed for simultaneous and dynamic in-plane and out-of-plane strain measurements. The shearography system is capable of measuring crack-tip deformation fields quantitatively. A spatial multiplexing technique based on Fourier transform is employed for simultaneous and dynamic multi-component phase retrieval. Two slit spatial filters and a common-path shearing interferometer are used to obtain an improved phase quality for crack-tip deformation measurements. Mode-I fracture experiments under three-point bending were conducted to validate the feasibility and the capability of this method.

  • Journal article
    Yetisen AK, Martinez-Hurtado JL, Uenal B, Khademhosseini A, Butt Het al., 2018,

    Wearables in Medicine

    , ADVANCED MATERIALS, Vol: 30, ISSN: 0935-9648
  • Journal article
    Yetisen AK, 2018,

    Biohacking

    , TRENDS IN BIOTECHNOLOGY, Vol: 36, Pages: 744-747, ISSN: 0167-7799

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