Emmanuil Rabinovich

Rapid prototyping of active microfluidic components based on magnetically modified elastomeric materials

Replica molding of elastomeric materials has proven to be an extremely useful new technology for the formation of complex microfluidic systems. Recent demonstrations of convenient methods for production of such systems by simple, rapid methods that do not require expensive fabrication facilities have enabled the extensive use of microsystems in research and development into a host of new application fields. This report describes a simple new method for fabricating active elastomeric components in microfluidic systems that is based on deformation of elastic materials that have been impregnated or coated with magnetic materials. Computer controlled miniature electromagnets are used to activate switching valves within microfluidics systems. Similar fabrication techniques can be easily extended to construct complex, and potentially completely integrated, microfluidic systems containing active valves, pumps, injectors, mixers, and flow controllers. Preliminary results indicate fabrication of channels approxima...

Fabrication of an integrated nanofluidic chip using interferometric lithography

The fabrication of nanoscale structures with dimensions approaching the scale of biological molecules offers approaches to the study of fluid dynamics and biomolecular transport. Ultimately, a parallel lithographic approach will be necessary if devices based on these nanofluidics are to achieve widespread availability and acceptance. We report on a flexible, all-optical lithography alternative that is amenable to large-scale production. We use interferometric lithography (IL) and anisotropic etching to produce large areas of parallel, nanofluidic channels with widths of ∼100 nm and depths of up to 500 nm. We also use standard optical lithography to create interfacing microchannels, such that the range of spatial scales on one chip varies by 104 (from mm scale reservoirs to 100 nm nanochannels). We provide initial demonstrations of capillary action and electrophoretic motion of fluorescent dye solutions.

Fluorescence biosensing strategy based on energy transfer between fluorescently labeled receptors and a metallic surface

A new fluorescence-based biosensor is presented. The biosensing scheme is based on the fact that a fluorophore in close proximity to a metal film (<100 A) experiences strong quenching of fluorescence and a dramatic reduction in the lifetime of the excited state. By immobilizing the analyte of interest (or a structural analog of the analyte) to a metal surface and exposing it to a labeled receptor (e.g. antibody), the fluorescence of the labeled receptor becomes quenched upon binding because of the close proximity to the metal. Upon exposure to free analyte, the labeled receptor dissociates from the surface and diffuses into the bulk of the solution. This increases its separation from the metal and an increase of fluorescence intensity and/or lifetime of the excited state is observed that indicates the presence of the soluble analyte. By enclosing this system within a small volume with a semipermeable membrane, a reversible device is obtained. We demonstrate this scheme using a biotinylated self-assembled monolayer (SAM) on gold as our surface immobilized analyte analog, fluorescently labeled anti-biotin as a receptor, and a solution of biotin in PBS as a model analyte. This scheme could easily be extended to transduce a wide variety of protein-ligand interactions and other biorecognition phenomena (e.g. DNA hybridization) that result in changes in the architecture of surface immobilized biomolecules such that a change in the separation distance between fluorophores and the metal film is obtained.

Phase-sensitive multichannel detection system for chemical and biosensor arrays and fluorescence lifetime-based imaging

Fluorescence lifetime-based sensors are attractive candidates to satisfy the demand for chemical detection and monitoring in medical, pharmaceutical, and environmental applications. In many cases it is desirable not only to monitor one particular chemical or biological species, but several simultaneously. In this work, we have focused our efforts on the development of a detection platform for multianalyte sensor arrays that is able to monitor changes in the fluorescence lifetimes corresponding to the presence of many analytes of interest in real time. We describe a new version of the multichannel, phase-sensitive electronic detection system employing a multianode photomultiplier tube, light emitting diodes, laser diodes, custom-built detection electronics, and a software package. This system utilizes the frequency-domain method of time-resolved spectroscopy. The present 16-channel prototype of the device is compact and assembled from inexpensive, off-shelf components. Future detection systems may be expec...

Technique for detecting changes in fluorescence lifetime by means of optoelectronic circuit auto-oscillation

We present a new, simple, inexpensive, and highly precise approach to excited-state fluorescence-lifetime-based measurements. The detection system consists of a closed-loop optoelectronic arrangement containing a radio frequency resonance amplifier, a fluorescence excitation light source, a fiber-optic delay line, and a photodetector. The system exhibits auto-oscillations in the form of intensity modulation. The oscillation frequency varies with the modulation phase shift of the fluorescent light. This frequency is used as the detection parameter, which is advantageous because frequency may be measured easily, inexpensively, and with high precision. This technique is well suited for chemical or biosensor applications.

Optoelectronic closed-loop auto-oscillator for fluorescence lifetime detection: a new fluorimetry technique with applications to chemical/biosensors

We present a new approach to excited state fluorescence lifetime-based measurements which is inexpensive and highly sensitive. The detection system consists of a closed-loop optoelectronic arrangement containing an intermediate frequency resonance amplifier, a fluorescence excitation light source (for example, a light emitting diode or a semiconductor laser), a fiber optic delay line, and a photodetector. The system exhibits self-oscillations in the vicinity of the frequency (Omega) approximately 1/(tau) (where (tau) is the excited state lifetime) which manifest themselves as modulation of the light. Changes in the excited state lifetime alter the phase delay of the loop, which in turn causes a frequency shift in the modulation signal. The frequency shift can be measured very precisely with a frequency counter. With appropriate averaging, this technique can yield sub-picosecond resolution of shifts in lifetime. This technique is suited for chemical/biological sensing applications, and can be easily duplicated for chemical/biological sensor arrays.

Fluorescence lifetime-based phase-sensitive sensor array with LED or diode laser excitation for chemical and biosensing

Fluorescence lifetime-based sensors are well-suited for chemical and biological applications since they are relatively insensitive to background light intensity, fluctuations and bleaching of fluorophores. Examples of applications include biosensing strategies where binding or a target analyte to an immobilized biological receptor molecule results in a change in the fluorescence lifetime of a fluorescent reporter group. It is desirable in many instances to have a sensor array to monitor the simultaneous binding of several analytes. We have designed a multichannel system using LEDs (or laser diodes) to excite fluorescence, multiple photodetectors, and a multichannel computer algorithm-based phase meter. The multichannel phase meter utilizes a PC and multichannel digital acquisition board. The resolution of each channel in the multichannel phase meter has been estimated at approximately 0.05 degrees. The eigen-phase fluctuations for each channel of the system are approximately 0.15 degrees, which allow us to estimate the lifetime resolution as better than 10 ps. We estimate the processing time of phase measurements for each channel as less than 200 ms. The usefulness of the system has been demonstrated in several operational examples, including a multichannnel pH meter and a fluoresphore competitive immunoassay-based chemical sensor.

Compact LED-based phase fluorimeter detection system for chemical and biosensor arrays

This paper describes a design for an inexpensive phase fluorimeter based on blue or green light emitting diodes for use with chemical and biological sensors with fluorescence and phosphorescence lifetime-based transduction. The phase fluorimeter is based on a personal computer, two frequency synthesizers and off-the-shelf optical and electronic components and has an estimated lifetime resolution better than 10 ps. The phase fluorimeter is especially well-suited for implementation with arrays of chemically sensitive elements. The data acquisition system allows rapid monitoring of light emission from fluors or phosphors immobilized in the chemically sensitive array elements, each of which can be designed to be responsive to a particular chemical analyte. This paper describes chemically sensitive elements based on ultrathin films of porous polymers and on self-assembled monolayers. The paper focuses on methods for detection of low levels of luminescence emission from micropatterned array elements that comprise sensor arrays. Of particular importance is the detection of low levels of fluorescence and phosphorescence from SAMs of alkanethiolates on thin gold and silver films. Methods for enhancing the luminescence yield from these SAMs include optimization of the dielectric environment of the luminescent dyes and surface plasmon resonance enhanced excitation.

Development of a new detection technique for fluorescence lifetime-based chemical/biological sensor arrays monitoring: dual closed-loop optoelectronic auto-oscillatory detection circuit

We present a new detection instrument for chemical/biological fluorescence lifetime-based sensors. The instrument comprises a primary, closed loop with a secondary loop controlling a variable phase delay within the primary loop. The primary loop consists of a fluorescence excitation light source, a fiber-optic delay line (with a gap for placement of a fluorescent sensor), an electronic phase shifter, a photo-detector, and a resonance-type RF amplifier. The secondary loop consists of a long-wavelength-pass optical filter, multimode fiber, a PMT, and an electronic phase detector (which is connected to the phase shifter of the primary loop). The system exhibits self-oscillations in the form of RF sinusoidal intensity modulation with frequency dependent on the fluorescence lifetime. Since the primary loop does not contain an optical filter, it is easier to obtain self-oscillations (compared to single loop systems). The feedback also improves the stability of the detection platform. The detection system is simple, inexpensive, and scalable for sensor array purposes. We demonstrate the use of a cost-effective, multi-channel, computer-algorithm-based frequency counter with this new system. We illustrate the detection capabilities of this detection system with the pH-sensitive, fluorescent probe carboxy seminaphthofluorescein (SNAFL-2) and an immunosensor based on fluorescence resonance energy transfer.

Dual closed-loop, optoelectronic, auto-oscillatory detection circuit for monitoring fluorescence lifetime-based chemical sensors and biosensors

We present a new detection instrument for sensor measurements based on excited-state fluorescence lifetimes. This system consists of a primary optoelectronic loop containing a resonance-type rf amplifier, a modulatable fluorescence-excitation light source, a fiber optic feedback loop (with a gap for a fluorescent sensor), and a photomultiplier tube. A secondary, phase-feedback optoelectronic circuit consists of a long-wavelength-pass optical filter, a second photomultiplier tube, a photodiode, an electronic phase detector, a dc amplifier, and an electronic phase shifter (inserted into the main loop). This phase-feedback circuit is new with respect to our previous work. Under the appropriate conditions, the main loop exhibits self-oscillations, manifesting themselves as sinusoidal rf modulation of light intensity. The phase-feedback circuit detects the modulation phase shift resulting from the finite excited-state lifetimes of a fluorophore. As the excited state lifetime changes, the phase shift from the electronic phase shifter also changes, which results in a shift in self-oscillation frequency. The detection system uses self-oscillation frequency as the detection parameter and has excellent resolution with respect to changes in excited-state lifetime ( approximately 1 ps). (c) 2004 Society of Photo-Optical Instrumentation Engineers.