Several new techniques are emerging to use digital display devices as new type of light source for analytical purpose.
We demonstrate the use of a liquid crystal display (LCD) computer screen as excitation light source for determining
gaseous oxygen contents over a relatively large area. Meso-scale device platforms are prepared with glass plates
incorporating fluidic channels and commercial oxygen sensor patches. Fluorophores are excited by blue wavelength
range from the LCD computer screen. The sensor signals exhibit a good linear relationship with respect to the oxygen
content. The display devices, with a capability of uniform illumination over a large area for variable wavelengths, have
a great potential as light source for high-throughput, multiple-analyte, quantitative chemical analysis.
We developed a simple oxygen imaging platform with phosphorescent oxygen sensor films to demonstrate a quantitative
oxygen determination method utilizing a color CCD camera. Phosphorescence quenching of a luminophore Pt(II) meso-tetrakis
(pentafluorophenyl) porphyrin complex (PtTFPP) immobilized in poly (dimethylsiloxane) (PDMS) matrix, is the
principal detection mechanism. This sensor material was cast to form a film on the bottom surface of a transparent Petri
dish. As levels of dissolved oxygen increased, phosphorescence of the complex decreased, allowing for measurement of
oxygen levels which developed in the sensor film. A camera with a charge-coupled device (CCD) was used in
conjunction with processing software to quantify oxygen levels colorimetrically. Microscopic images were collected
using a CCD camera and stored as a set of red/green/blue (RGB) images. Phosphorescence excitation (390 nm peak) is
limited to the blue (B) pixels of the CCD chip, and these values were discarded; while retaining the oxygen-responsive
phosphorescence emission (645 nm peak) almost identical with the response range of the red (R) pixels. Red pixel
intensity analysis effectively extracts color intensity information, which can be in turn directly related to oxygen
contents. Color CCD cameras allow simultaneous acquisition of many types of chemical information by combining the
merits of digital imaging with the attributes of spectroscopic measurement. Therefore, use of color CCD cameras is
considered as an inexpensive alternative to time-resolved imaging for relatively short-term monitoring.
In this work, a novel photopatternable hydrogel-based material for the fluorescent detection of hydrogen peroxide was
developed and studied as a possible sensing element in optical biosensors. This composite hydrogel material was
developed to maximize analyte transport, be amenable to existing microfabrication techniques, and dovetail with various
enzyme immobilization strategies. Nanoparticles loaded with a hydrogen peroxide sensitive europium tetracycline
complex (EuTc) were mixed with monomer and crosslinker to form a photopolymerizable precursor. Sensitivity to
glucose can be introduced through addition of methacrylated glucose oxidase into the precursor solution, allowing for
covalent immobilization of the enzyme. As a result, the material can be integrated directly into optical biosensors for
continuous glucose monitoring.
A new method of color pixel intensity analysis to obtain an oxygen concentration is presented in this research. Until
recently, color charge coupled devices (CCDs) have rarely been used for oxygen imaging in spite of its usefulness for
analyzing the spectral content of images. The proposed new method involves extracting the red color element to enhance
oxygen-related information and eliminate distorted green color information from the color images of the sensors. A
commercial RedEyeTM oxygen sensor patch was used to verify this method. The linearity and sensitivity of oxygen
detection based on the red intensity analysis was improved to those of spectrometric measurement and total color
intensity analysis. This method also has potential applications in other luminescence sensors and simultaneous structural
and functional imaging of biological systems.
Optical sensors are a common tool to measure the dissolved oxygen concentration in environmental, industrial and
medical areas. Much effort has been put on developing and using novel optical dyes and materials used as the
immobilization matrixes. A poly (ethylene glycol) (PEG)-rich hydrogel was used as a fluorophore matrix. For optical
sensor applications, this hydrogel was chemically anchored on negative-tone photopolymer SU-8 surface through a free
radical reaction in which 1-hydroxycyclohexyl phenyl ketone (HCPK) served as the surface bound photoinitiator.
Dissolved oxygen concentrations were detected based on the fluorescent intensity at emission wavelength of a
fluorophore, dichlorotris (1, 10-phenanthroline) ruthenium (II) hydrate 98%, toward dissolved oxygen molecules. The
normal characteristics of optical dissolved sensor were measured and recorded. All the results indicate the potential use
of patternable polymerized PEGDA membranes, which is chemically anchored to SU-8 surface, as an ideal candidate
matrix based on polymeric channel structures
A dry film photoresist (MX 5020 from DuPont Electronic Technologies) was selected to fabricate microstructures with
high sidewall verticality. Sidewall verticality of dry film is very important for better pattern transfer and sharp features.
A fractional factorial design (FFD) method was used to identify the significant process variables for sidewall
optimization. The most significant factor was determined to be exposure energy, as other factors were not significant in
improving sidewall verticality. It was found that the sidewall slope increased with a decrease in exposure energy. The
fabricated dry film molds with nearly vertical sidewalls (86°) were used for copper electroplating and sputter deposited
Ti lift-off applications. The electroplating process was also optimized using a fractional factorial design. A lower plating
current density resulted in a smoother, fine grained deposit compared to the higher current density, and the dry film resist
was able to withstand a very acidic (pH ~1) copper sulfate plating solution. Sputtered titanium films with a thickness of
200 nm were also successfully lifted-off using dry film patterning.
Due to the proper optical property and flexibility in the process development, an epoxy-based, high-aspect ratio
photoresist SU-8 is now attracting attention in optical sensing applications. Manipulation of the surface properties of SU-8 waveguides is critical to attach functional films such as chemically-sensitive layers. We describe a new integration
process to immobilize fluorescence molecules on SU-8 waveguide surface for application to intensity-based optical
chemical sensors. We use two polymers for this application. Spin-on, hydrophobic, photopatternable silicone is a
convenient material to contain fluorophore molecules and to pattern a photolithographically defined thin layer on the
surface of SU-8. We use fumed silica powders as an additive to uniformly disperse the fluorophores in the silicone
precursor. In general, additional processes are not critically required to promote the adhesion between the SU-8 and
silicone. The other material is polyethylene glycol diacrylate (PEGDA). Recently we demonstrated a novel photografting
method to modify the surface of SU-8 using a surface bound initiator to control its wettability. The activated surface is
then coated with a monomer precursor solution. Polymerization follows when the sample is exposed to UV irradiation,
resulting in a grafted PEGDA layer incorporating fluorophores within the hydrogel matrix. Since this method is based
the UV-based photografting reaction, it is possible to grow off photolithographically defined hydrogel patterns on the
waveguide structures. The resulting films will be viable integrated components in optical bioanalytical sensors. This is a
promising technique for integrated chemical sensors both for planar type waveguide and vertical type waveguide
chemical sensors.
We present an intelligent microfluidic system with oxidase enzyme coupled biosensors. Baseline (zero-value) drift and
sensitivity degradation are two common problems related with biosensors. In order to overcome these problems there is a
great need for integrating an on-demand, in situ self-diagnosis and self-calibration unit along with the sensor. Utilizing
the microfluidic technology, we explore the feasibility of implementing this function without any externally coupled
bulky apparatus. A microsystem including a microfluidic channel and calibration electrodes are prepared by
microfabrication techniques. A novel method of using hydrogen and oxygen bubbles generated by electrolysis of water is
used to saturate the solution with these gases in the microfluidic channel where the biosensor is placed. The hydrogen
bubble provides oxygen-depleted microenvironment to conduct a zero-value calibration procedure for the sensor. The
oxygen bubble provides high sensitivity and constant oxygen background environment to allow stable enzyme reactions
that is not limited or perturbed by the fluctuation of background oxygen in sample solutions. Commercial oxygen
sensors and pH sensors are used to confirm whether saturation or depletion of oxygen has occurred with minimum local
pH change near the sensor during the electrolytic bubble generation. The glucose data obtained from the experiments
assure that our proposed method is promising to overcome the above mentioned two problems.
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