Spectrometers are instruments that are used to measure different optical properties such as transmittance, absorbance, and concentration of liquid and solid samples. The standard spectrometers are big, bulky, nonportable, and costly. This makes them inaccessible to integrate into portable devices. We have developed a handheld low-cost camera-based spectrometer. It consists of a camera, direct vision spectroscope, and Raspberry Pi board. The components are enclosed in a 3D-printed structure. The spectrometer is calibrated using laser light sources. In liquid samples, when the light from the source passes through the sample and the transmitted light passes through the direct vision spectroscope, a spectrum is formed. The spectrum seen in the direct vision spectroscope is captured by the camera and processed using a Raspberry Pi board using a Python program. The results can be displayed in a graphical user interface in the mobile phone or computer connected wirelessly to the Raspberry Pi board. Based on the wavelength range of light source, the absorbance spectrum in the visible region can be measured using the spectrometer. The absorbance of different concentrations of food color samples are measured and compared with the standard spectrometer. The results of the device are comparable with the standard spectrometer.
Fluorescent lateral flow assays (LFA) strips have gained popularity for medical diagnostics application by offering fast and reliable response in both qualitative and quantitative readout formats. The fluorescence emission is generated when excited with appropriate optical source, and is dependent on the analyte concentration in the sample spotted on the LFA strips. Quantitative detection requires a LFA reader to carry out accurate and precise measurements of the fluorescence emission. These readers can be of either benchtop or handheld type, and conventionally use either photo multiplier tube (PMT) or avalanche photodiodes (APD) or customized photo diodes. In addition to their proven benefits like high sensitivity, speed and gain, the availability of silicon photomultipliers (SiPM) in micro form factor makes them good choice for developing miniaturized LFA strip readers. In this study, a portable fluorescence reader using SiPM sensor has been designed, which records the fluorescence intensity of the spot on planar surfaces e.g. nitrocellulose membrane (NCM) packaged in the plastic cases. The design and operation details of the benchtop reader using SiPM sensor along with excitation source, focusing and collimating optics and power supplies integrated with general purpose microcontroller board in a mechanical housing are reported in this paper. The testing of the developed reader is done by using mercaptopropionic acid capped cadmium telluride quantum dots (MPA-CdTe QDs) as the fluorescent analytes spotted on NCM packaged plastic strips. The results obtained from the developed portable reader are compared with the standard fluorescence plate reader for QD concentration varying from 60 μg/mL to 420 μg/mL and are found to be in good accordance with the response and resolution of the conventional fluorescent plate reader. Further work is under development for testing the developed reader for disease diagnostic applications.
Synthesis of quantum dots (QDs) in aqueous medium is advantageous as compared to the organic solvent mediated
synthesis, as the aqueous synthesis is less toxic, reagent effective, easily reproducible and importantly, synthesized QDs
have biological compatibility. The QDs should be aqueous in nature for use in cell imaging, drug labeling, tracking and
delivery. Structural modifications are necessary to enable their use in biosensing application. In this work,
mercaptopropionic acid capped cadmium telluride QDs (MPA-CdTe QDs) were synthesized by hydrothermal method
and characterized by various techniques. Water and various biochemical buffers were used to study the fluorescence
intensity stability of the QDs at different physicochemical conditions. QDs stored in 4° C showed excellent stability of
fluorescence intensity values as compared to the samples stored at room temperature. Staphylococcal protein A (SPA)
was conjugated with the QDs (SPA-QDs) and characterized using UV and fluorescence spectroscopy, zeta potential,
HRTEM, FTIR, and AFM. Blue shift was observed in the fluorescence emission spectra that may be due to reduction in
the surface charge as carboxyl groups on QDs were replaced by amino groups of SPA. This SPA conjugated to QDs
enables binding of the C-terminal of antibodies on its surface allowing N-terminal binding site remain free to bind with
antigenic biomarkers. Thus, the biosensor i.e. antibody bound on SPA-QDs would bind to the antigenic biomarkers in
sample and the detection system could be developed. As QDs have better fluorescence properties than organic dyes, this
biosensor will provide high sensitivity and quantitative capability in diagnostics.
Chemotherapy Induced Nausea and Vomiting (CINV) is a serious health concern in the treatment of cancer patients. Conventional routes for administering anti-emetics (i.e. oral and parenteral) have several drawbacks such as painful injections, poor patient compliance, dependence on skilled personnel, non-affordability to majority of population (parenteral), lack of programmability and suboptimal bioavailability (oral). Hence, we have developed a trans-epidermal antiemetic drug delivery patch using out-of-plane hollow silicon microneedle array. Microneedles are pointed micron-scale structures that pierce the epidermal layer of skin to reach dermal blood vessels and can directly release the drug in their vicinity. They are painless by virtue of avoiding significant contact with dermal sensory nerve endings. This alternate approach gives same pharmacodynamic effects as par- enteral route at a sparse drug-dose requirement, hence negligible side-effects and improved patient compliance. Microneedle design attributes were derived by systematic study of human skin anatomy, natural micron-size structures like wasp-sting and cactus-spine and multi-physics simulations. We used deep reactive ion etching with Bosch process and optimized recipe of gases to fabricate high-aspect-ratio hollow silicon microneedle array. Finally, microneedle array and polydimethylsiloxane drug reservoir were assembled to make finished anti-emetic patch. We assessed microneedles mechanical stability, physico-chemical properties and performed in-vitro, ex- vivo and in-vivo studies. These studies established functional efficacy of the device in trans-epidermal delivery of anti-emetics, its programmability, ease of use and biosafety. Thus, out-of-plane hollow silicon microneedle array trans-epidermal antiemetic patch is a promising strategy for painless and effective management of CINV at low cost in mainstream healthcare.
Urea is an important biomarker for identification of kidney diseases. Early urea detection using a specific and sensitive technique can significantly reduce the mortality of patients. The research aims at developing fluorescence-based FITCmediated pH and urea measurement. A system containing FITC-dextran in alginate microspheres was developed using air-driven atomization. pH/Urea biosensor was characterized using optical microscopy, SEM, and CLSM. Urea biosensing studies were performed by exposing different standard solutions of pH and urea standard solutions using fluorescence spectroscopy (λex=488 nm and λem=520 nm). FITC-dextran was entrapped using an encapsulation unit and alginate microspheres were formed. The microspheres were found to be uniform and spherical in nature with sizes (50±10μ). FITC-dextran was found to be uniformly distributed in the alginate microspheres as per the CLSM scans. Urea biosensing studies indicate that a linear correlation was observed with increasing urea concentrations. The said microspheres can be used to detect changes in pH from 4-8 units owing to its linear response in this range. FITC dextran loaded alginate microspheres showed an improved range of detection upto 7 mM in comparison to 1.5 mM when in solution phase in a study with urea concentrations from 0-50 mM. The pH and urea detection was accurate to an extent of interday variation of 5%. FITC-dextran loaded alginate microspheres show a great potential for usage as a pH and urea biosensor for early detection of kidney diseases.
Clinically glucose monitoring in diabetes management is done by point-measurement. However, an accurate, continuous glucose monitoring, and minimally invasive method is desirable. The research aims at developing fluorescence-mediated glucose detecting biosensors based on near-infrared radiation (NIR) oxygen sensitive dyes. Biosensors based on Glucose oxidase (GOx)-Rudpp loaded alginate microspheres (GRAM) and GOx-Platinum-octaethylporphyrin (PtOEP)-PLAalginate microsphere system (GPAM) were developed using air-driven atomization and characterized using optical microscopy, CLSM, fluorescence spectro-photometry etc. Biosensing studies were performed by exposing standard solutions of glucose. Uniform sized GRAM and GPAM with size 50±10μm were formed using atomization. CLSM imaging of biosensors suggests that Rudpp and PtOEP nanoparticles are uniformly distributed in alginate microspheres. The GRAM and GPAM showed a good regression constant of 0.974 and of 0.9648 over a range of 0-10 mM of glucose with a high sensitivity of 3.349%/mM (625 nm) and 2.38%/mM (645 nm) at 10 mM of glucose for GRAM and GPAM biosensor. GRAM and GPAM biosensors show great potential in development of an accurate and minimally invasive glucose biosensor. NIR dye based assays can aid sensitive, minimally-invasive and interference-free detection of glucose in diabetic patients.
A broadband tunable filter for the infrared spectral region is desired for use as a wavelength selective element in a miniature absorption spectrometer. We present the design, fabrication, packaging, and characterization of a bulk micromachined Fabry-Perot interferometer (FPI) for meeting this need. A novel approach to fabricate a MEMS-based tunable resonant cavity using two separate wafers bonded using a "lock-and-key" spacer design is outlined, with the goal of realizing electrostatically actuated membranes from films predeposited on base substrates. This ability could enable the pursuit of MEMS devices without in-house chemical vapor deposition (CVD) capability, after overcoming the shortcomings of bulk micromachining. The FPI device was designed with a planar structure comprising two face-to-face bonded chips of overall lateral dimension 10×10 mm with deflection regions of 2×2 mm. The device employs electrostatic actuation to tune the output wavelength, for which finite element modeling predicted low (<1 V) actuation voltages for movement of the membrane. Experimental results from device testing (mechanical) were found to differ from the theoretical predictions, primarily due to fabrication issues. Specifically, the device performance was found to be greatly influenced by the amount of residual silicon on the wafer chip following inductively coupled plasma (ICP) backside etching, with high voltages (~30 times higher than modeled) required for actuation of the device. Through a combination of modeling and experimental measurements, it is demonstrated that the ability to produce MEMS devices by releasing membranes from films predeposited on substrates is highly susceptible to error in etching and packaging.
Components of a microspectrometer for operation in the IR range has been designed, fabricated, and characterized. An adjustable Fabry-Perot interferometer is used to select the resonant frequency of the system through electrostatic actuation, allowing tuning for certain optical frequencies to pass. Silicon microfabrication techniques are employed for the fabrication of the device. The intended use of the device is for spectroscopic study of liquids in biomedical and environmental applications; therefore, a sample containment chamber has been integrated into the device. The device was designed using finite element modeling to determine the stress distribution on the silicon nitride membrane due to deflection and the voltage required for the suitable displacement of the membrane to which one mirror is attached. The devices have been fabricated using a combination of processing steps to sputter gold mirrors on nitride membranes, to deposit electrodes and spacers using evaporation and photosensitive polyimide, to etch channels and sacrificial layers, and to bond chips to obtain a resonant cavity. Optical characterization was performed with an FTIR spectrometer. Initial results presented here support the feasibility of the approach in developing standalone microspectrometers for analysis of aqueous samples including biological fluids.
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