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Presbyopia, an age-related ocular disorder, is characterized by the loss in the accommodative abilities of the human ocular system and afflicts more than 1.8 billion people world-wide. Conventional methods of correcting presbyopia fragment the field of vision, inherently resulting in significant vision impairment. We demonstrate the development, assembly and evaluation of autofocusing eyeglasses for restoration of accommodation without vision field loss. The adaptive optics eyeglasses consist of two variable-focus piezoelectric liquid lenses, a time-of-flight range sensor and low-power, dual microprocessor control electronics housed within an ergonomic frame. Patient-specific accommodation deficiency models were utilized to demonstrate a high-fidelity accommodative correction. Each accommodation correction calculation was performed in ~67 ms requiring 4.86 mJ of energy. The optical resolution of the system was 10.5 cycles/degree, featuring a restorative accommodative range of 4.3 D. This system can run for up to 19 hours between charge cycles and weighs ~132 g, allowing comfortable restoration of accommodative function, 12 pages, 13 figures

Wearable eye tracking devices have broad uses in medicine, psychology, augmented & virtual reality and consumer market research. Most mobile eye trackers available today utilize infrared imaging of the pupil and corneal reflections with video cameras. This tracking method requires sophisticated real-time processing of video signals consuming substantial electrical power. This method is thus unsuitable for light weight wearables such as adaptive smart eyeglasses for correction of presbyopia. In this paper we present a low-profile, low-power (7.7 mJ/sample) digital eye tracker oculometer based on infrared sclera tracking. The system is implemented using eight, 24-bit infrared proximity sensors and synchronous infrared LEDs. The pupil location is determined from 32 reflected pulsed light measurements independent of ambient illumination. The digital oculometer is 3.1 mm thick and weighs ~3 g. The tracker mounts adjacent to the tunable lenses in the smart eyeglasses frame. The eye tracker showed a pointing error of 1.3 degrees rms over a vertical and horizontal range of 30 degrees when tested by an observer.

Liquid-filled tunable-focus lenses have been demonstrated to be suitable for autofocus eyewear applications. Traditionally, these lenses are constructed using an elastomeric polymer chamber filled with a high-index liquid. In this work, we investigate the effect of elastomeric creep on the deformation and eventual degradation of these tunable lenses. We use numerical analysis of a deformable circular disk representative of the lens and provide rigorous experimental results testing the creep property of a number of elastomers. Finally, we provide a comparative study of different elastomeric materials and select the best one for this application.

More than 100 million people in the United States of America alone suffer from age-related presbyopia caused by a loss of focal accommodation of the eye crystalline lens as the lens stiffens with age. The resulting accommodative error or lag produces blurred images of objects placed at different distances. Conventional fixed uniform or graded power eyeglasses cannot provide accommodation thus resulting in significant visual impairment. In this paper we will discuss the implementation of lightweight auto-focusing eyeglasses that augment the accommodative range thus partially or fully restoring normal vision function. The paper discusses some aspects of the construction of tunable power eyepieces and the implementation of accommodation correction algorithms.

Over 1 billion people worldwide including more than 100 million people in the United States of America alone suffer from an age-related eye condition known as presbyopia. Presbyopia is caused by a loss of focal accommodation of the crystalline lens inside the eye as the lens stiffens with age. A presbyopic person has reduced or very limited ability to focus on objects placed at different distances. The utilization of conventional fixed, uniform or graded power eyeglasses for presbyopia correction is generally unsatisfactory as fixed power eyepieces cannot provide any accommodation restoration. In this paper we will discuss an implementation of lightweight adaptive-optics auto-focusing eyeglasses that augment the accommodation range of vision thus partially or fully cancelling the accommodation loss caused by presbyopia and restoring normal vision function.

Crystalline cubic silicon carbide (3C-SiC) nanopowders were synthesized using hexamethyldisilane (HMDS) in a resistance heated chemical vapour deposition (CVD) reactor. The effects of different diluent gases on the synthesis of the SiC powder were also studied. The deposited powder was characterized using high-resolution X-ray diffraction (HRXRD) analysis, transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and BET surface area measurements. The crystallite size was estimated to be in the range of nanometer (10–20 nm) from XRD data and the particle size (∼10–30 nm) was obtained by TEM, HRTEM and BET. The growth condition was optimized in terms of crystallinity, chemical composition and deposition rate by varying different parameters such as the diluent gas (H2/Ar ratio) and temperature.

Over the course of last two decades, surface plasmon resonance (SPR) has emerged as a viable candidate for label-free detection and characterization for a large pool of biological interactions, ranging from hybridization of oligonucleotides to high throughput drug-screening. Conventional SPR bio-sensing involves a step-response method where the SPR sensorgram in response to a switched sequential flow of analyte and buffer is plotted in real-time and fitted to an exponential curve to extract the associative and dissociative reaction rates. Such measurement schemes involve continuous flow conditions where a substantial reagent volume is consumed and is subject to dispersive mixing at flow switching zones. In this paper, we demonstrate a new plug-train SPR technique in a microfluidic chip that separates and singulates solvent plugs in analyte and buffer by an immiscible air phase. Bio-samples are first discretized within plug droplets with volumes in order of few hundred nanoliters or less followed by pressure-driven transport onto SPR sensing sites of this hydrophobically modified SPR microdevise. The kinetic constants ka and kd for a model protein-small molecule interaction pair are extracted from a plug-train signal and are shown to be in reasonable agreement with our previous reports.

We demonstrate a new dual slope SPR technique that is ten-fold faster than the conventional step-response method. The new scheme utilizes rapid slope-based measurements followed by rapid reset, and it separates association and dissociation half reaction measurements at two separate sites inside a dual-chamber PDMS microfluidic chip. For a model CAII-ABS test system, the association and dissociation slopes were measured in 30 seconds compared to 5 minutes for step-response. The values of k(a) and k(d) calculated from the slope method are 3.66 ± 0.19 × 10(3) M(-1) s(-1) and 4.83 ± 0.17 × 10(-2) s(-1), respectively, matching well with step-response values while facilitating ~10 to 15 fold faster detection and quantification.

Label-free techniques such as surface plasmon resonance (SPR) have used a step-response excitation method to characterize the binding of two biochemical entities. A major drawback of the step response technique is its high susceptibility to thermal drifts and noise which directly determine the minimum detectable binding mass. In this paper we present a new frequency-domain method based on the use of multisine chemical excitation that is much less sensitive to these disturbances. The multisine method was implemented in a PDMS microfluidic chip using a dual channel, dual multiplug chemical signal generator connected to functionalized and reference SPR binding spots. Kinetic constants for the reaction are extracted from the characteristics of the sense spot response versus frequency. The feasibility of the technique was tested using a model system of Carbonic Anhydrase-II analyte and amino-benzenesulfonamide ligand. The experimental signal to noise ratio (SNR) for the multisine measurement is about 32 dB; 7 dB higher than that observed with the single step-response method, while the overall measurement time is twice as long as the step method.

New developments in microfluidic chip technology enable the construction of chemical spectrum analyzers that can probe the binding interactions between chemical entities. In this paper we report the implementation of a microfluidic chip suitable for Fourier transform measurements of biochemical interactions. The chip consists of a chemical signal generator, a flow cell and a binding sensor surface. The microfluidic signal generator produces a periodic stream of protein plugs in solution flowing at constant velocity through the cell. This flow produces periodic association and dissociation cycles of the protein to a functionalized gold sensing surface placed inside the cell. The sensor activity corresponding to the phasor response of the chemical interaction at the excitation frequency is measured optically using surface plasmon resonance (SPR) imaging. We demonstrated the feasibility of the technique using a model system of carbonic anhydrase-II (CA-II) and immobilized 4-(2-Aminoethyl) benzenesulfonamide (ABS) ligand. The observed transfer function showed a dominant pole at 10.2 mHz corresponding to association and dissociation constants of 4.8 × 10(3) M(-1)·s(-1), and 3.5 × 10(-2) s(-1) respectively.

Surface plasmon resonance (SPR) is a popular technique for label-free detection of biomolecular interactions at a surface. SPR yields quantitative kinetic association and dissociation constants of surface interactions such as the binding of two molecular species, one present in the liquid phase and the other immobilized at the surface. Current state-of-the-art SPR systems extract kinetic constants from measurements of the step response of the interaction versus time. The step response measurement is subject to the influence of noise and drift disturbances that limit its minimum-detectable mass changes. This paper presents a new SPR technique that measures the biomolecular interaction not in time but over a very narrow frequency range under periodic excitation. The measured response is, thus, locked to a very specific narrow band signal. This narrow band spectral sensing scheme has a very high degree of rejection to uncorrelated spurious signals. The signal-locked SPR technique was implemented using a chemical modulator chip connected to a set of functionalized Au sensing sites downstream. Binding experiments for a model system of carbonic anhydrase-II (CA-II) analyte and immobilized 4-(2-aminoethyl)benzenesulfonamide (ABS) ligand display a 100-fold (20 dB) improvement in the measured signal-to-noise ratio (SNR) when using the new technique compared to the SNR achieved using the conventional step response method.

Surface plasmon resonance (SPR) is a widely used label-free detection technique that has many applications in drug discovery, pharmacokinetics, systems biology and food science. The SPR technique measures the dynamics of a biomolecular interaction at a surface, yielding kinetic association and dissociation constants. Present SPR systems measure the step response of the interaction in time domain hence are subject to time-varying noise disturbances and drifts that limit the minimum-detectable mass changes. This paper presents a new synchronous SPR technique that measures the biomolecular interaction not in time domain, but in frequency domain with a high degree of rejection to uncorrelated spurious signals. The new technique was implemented using a PDMS microfluidic chemical signal modulator chip connected to a set of on-chip functionalized Au SPR sensing sites. Preliminary experimental spectral data for a model system of carbonic anhydrase binding demonstrates the feasibility of the new spectral technique.

A new frequency domain SPR technique for quantitative measurement of biomolecular interactions is presented with the goal of improved signal-to-noise ratio. The technique uses a microfluidic chemical modulator chip with Au sensing sites.