Time-Resolved Measurements in Optoelectronic Microbioanalysis

A report presents discussion of time-resolved measurements in optoelectronic microbioanalysis. Proposed microbioanalytical laboratory-on-a-chip devices for detection of microbes and toxic chemicals would include optoelectronic sensors and associated electronic circuits that would look for fluorescence or phosphorescence signatures of multiple hazardous biomolecules in order to detect which ones were present in a given situation. The emphasis in the instant report is on gating an active-pixel sensor in the time domain, instead of filtering light in the wavelength domain, to prevent the sensor from responding to a laser pulse used to excite fluorescence or phosphorescence while enabling the sensor to respond to the decaying fluorescence or phosphorescence signal that follows the laser pulse. The active-pixel sensor would be turned on after the laser pulse and would be used to either integrate the fluorescence or phosphorescence signal over several lifetimes and many excitation pulses or else take time-resolved measurements of the fluorescence or phosphorescence. The report also discusses issues of multiplexing and of using time-resolved measurements of fluorophores with known different fluorescence lifetimes to distinguish among them

Method and apparatus for distributed sensing of volatiles using a long period fiber grating sensor with modulated plastic coating for environmental monitoring

Optical time domain reflectometry caused by absorption of a volatile or analyte into the fiber optic cladding is used as an optical nose. The fiber optics (14) are covered with a gas permeable film (44) which is patterned to leave millimeter wide gas permeable notches (48a-48d). The notches contain a sensing polymer that responds to different gases by expanding or contracting

Mass spectrometer calibration of Cosmic Dust Analyzer

The time of flight mass spectrometer of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft, is expected to be placed in orbit about Saturn to sample the ring material and satellite impact ejecta. Upon impact of an incident dust particle against the target plate at velocities of 5-100 km/s, some 10–8 to 10–5 times the particle mass of positive valence, single-charged ions is induced. These are analyzed via a time-of-flight mass spectrometer. Initial experiments employing a pulsed N2 laser (>300 µJ/pulse, 4ns, 337nm) acting on a suite of samples are described. The laser beam is focussed to deliver the light pulses onto a laser power density (1011 W/cm2) to simulate the impact of particles. Laser ionization produced a charge of 4.6 pC per pulse for aluminum alloy. Estimating that each Al+1 ion require energy of 5.98 eV ionization energy/ion implies that 10–5% of the laser energy produced ions and the present system has a 5% efficiency of collecting the laser-irradiation induced ions. Employing a multi-channel plate detector in this mass spectrometer yields for Al-Mg-Cu alloy and kamacite (Fe-Ni mineral) targets well defined peaks at 24 (Mg+1), 27 (Al+1) and 64 (Cu+1), and 56 (Fe+1), 58 (Ni+1) and 60 (Ni+1) dalton, respectively

Method and apparatus for chemical and topographical microanalysis

A scanning probe microscope is combined with a laser induced breakdown spectrometer to provide spatially resolved chemical analysis of the surface correlated with the surface topography. Topographical analysis is achieved by scanning a sharp probe across the sample at constant distance from the surface. Chemical analysis is achieved by the means of laser induced breakdown spectroscopy by delivering pulsed laser radiation to the sample surface through the same sharp probe, and consequent collection and analysis of emission spectra from plasma generated on the sample by the laser radiation. The method comprises performing microtopographical analysis of the sample with a scanning probe, selecting a scanned topological site on the sample, generating a plasma plume at the selected scanned topological site, and measuring a spectrum of optical emission from the plasma at the selected scanned topological site. The apparatus comprises a scanning probe, a pulsed laser optically coupled to the probe, an optical spectrometer, and a controller coupled to the scanner, laser and spectrometer for controlling the operation of the scanner, laser and spectrometer. The probe and scanner are used for topographical profiling the sample. The probe is also used for laser radiation delivery to the sample for generating a plasma plume from the sample. Optical emission from the plasma plume is collected and delivered to the optical spectrometer so that analysis of emission spectrum by the optical spectrometer allows for identification of chemical composition of the sample at user selected sites

Scanning probe chemical and topographical microanalysis

The last decade has seen a rapid rise of Scanning Probe Microscopy, SPM, as a prominent and versatile approach for surface studies. SPM instruments are differentiated from the beam-based ones by the fact that they use solid proximal probes for localized analysis. The most commonly used SPM methodology is Atomic Force Microscopy, AFM. In its basic implementation, AFM provides topographical information with nanometer resolution. The most common modifications allow the magnetic, electrostatic, and specific chemical environment to be examined. However, there is no direct way today to perform general chemical analysis with AFM probes. Near-field Scanning Optical Microscopy, NSOM, is another variation of SPM where sharp tapered optical fibers serve dual purposes, being proximal probes of sample topography, and providing the means for localized light delivery for optical studies with sub-wavelength spatial resolution. Again, NSOM itself does not have a general chemical contrast capability. However, the capability to deliver light to localized area opens the way to a multitude of experiments that can be devised using different aspects of light interaction with the sample. This thesis demonstrates several approaches for combined topographical and chemical investigations. Infrared spectroscopy is a sensitive molecular analysis tool. Without scanning proximal probe, IR microscopy has very poor spatial resolution. Enabling methodology for probe fabrication for Near-field Scanning Infrared Microscopy, NSIM, is presented. The efforts in combining NSOM with mass spectrometry, which is probably the most general chemical analysis tool, are outlined. We have demonstrated the possibility of simultaneous topographical and molecular imaging. Another variation of chemical imaging is the combination of SPM and Laser Induced Breakdown Spectroscopy, LIBS. In this method the elemental composition of samples is obtained by analyzing optical emissions from transient plasma plumes formed by intense laser pulses delivered through fiber probes. We have demonstrated the feasibility of this approach. The instrument that we have developed is an attractive complementary tool for established methods of spatial elemental analysis, such as X-ray Fluorescence. Among its attractive features are operation in ambient conditions, minimal requirements for sample preparation, and ease of use

Topographical and Chemical Microanalysis of Surfaces with a Scanning Probe Microscope and Laser-Induced Breakdown Spectroscopy

Spatially resolved chemical imaging is achieved by combining a fiber-optic scanning probe microscope with laser-induced breakdown spectroscopy in a single instrument, TOPOLIBS. Elemental composition of surfaces can be mapped and correlated with topographical data. The experiment is conducted in air with minimal sample preparation. In a typical experiment, surface topography is analyzed by scanning a sharp fiber-optic probe across the sample using shear force feedback. The probe is then positioned over a feature of interest and pulsed radiation is delivered to the surface using a nitrogen laser. The pulse vaporizes material from the surface and generates a localized plasma plume. Optical emission from the plume is analyzed with a compact UV/visible spectrometer. Ablation crater size is controlled by the amount of laser power coupled into the probe. Sampling areas with submicrometer dimensions are achieved by using reduced laser power

Mass spectrometer calibration of high velocity impact ionization based cosmic dust analyzer

We are calibrating the time of flight mass spectrometer of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft. The CDA measures the flux of particles in the 10^(−15) to 10^(−9) g range at intersection velocities of up to 100 km/s. Of special interest are the chemical composition of the particles in orbit about Saturn and/or its satellites that are expected to be captured by CDA during ring plane crossings and upon close encounter with the satellites. Upon impacting a rhodium plate, particles are expected to partially ionize and their chemical composition is expected to be determined from mass analysis of the positive ions. In order to optimize impact ionization calibration experiments using a light gas-gun launched microspheric particles, we have done initial testing with a short duration pulsed laser (4 ns duration nitrogen laser (337 nm)). The beam is focused to deliver the 300μJ energy per laser pulse onto a 33 μm^2. The laser power density (≈10^10 W/cm^2) simulates the impact of particles with various combinations of density and velocities, e.g., 8 g/cm^3 (Fe) projectile at 23 km/s or 1 g/cm^3 projectile at 65 km/s. The CDA spectrometer will operate in the near vacuum of Saturnian zone environment is housed in a laboratory chamber at 10^(−6) mbar. The ions and electrons are separated by 680 V between target and grid. The laser ionization produces charge of 4.6pC (mostly Al^(+1)) in aluminum and 2.8pC (Fe^(+1)) in stainless steel. Estimating that each Al^(+1) and Fe^(+1) ion requires an energy of 5.98 and 7.90 eV/ion implies that ∼10−5 % of the laser pulse energy produces ions and the present system has a 10% detection efficiency. Using multi-channel plate detector to detect ions from aluminum alloy and kamacite yields well defined peaks at 24(Mg^(+1)), 27(Al^(+1)) and 64 (Cu^(+1)), and, 56(Fe^(+1)), 58(Ni^(+1)) and 60(Ni^(+1)) amu, respectively. Also contaminant ions at 23 (Na^(+1)) and 39(K^(+1)) amu are detected