Optical Particle Detection Research Articles

Design and evaluation of a condensation particle counter with high performance for single-particle counting

A full-flow butanol-based condensation particle counter (CPC) with a concentration range from 0 to 2 × 105 particles/cm3 was developed to measure nanoparticles down to 4.5 nm. Good single-particle counting performance was achieved by developing a high-speed optical particle detection module. The pulse width of single particle was approximately 1.2 μs at a flow rate of 0.3 L/min. By establishing a heat and mass transfer model using the COMSOL simulation software, the effects of temperature and aerosol sampling flow on the condensation growth of nanoparticles were studied. The performance of developed condensation particle counter was evaluated through a series of experiments to determine the coincidence probability, concentration range, and detection efficiency (cutoff diameter). At concentrations of 1.5 × 104 particles/cm3 and 2 × 105 particles/cm3, the coincidence probabilities of the developed condensation particle counter were 9.5% and 55%, respectively. A 99.9% (R2) statistical correlation was obtained between the pulse-time corrected concentration of the developed condensation particle counter and the standard reference concentration. Finally, the experimental results showed that the developed condensation particle counter cutoff diameter, at which the detection efficiency was 50%, for sucrose aerosol particles was 4.5 nm.

Evaluating the influence of laser wavelength and detection stage geometry on optical detection efficiency in a single-particle mass spectrometer

Abstract. Single-particle mass spectrometry (SPMS) is a useful tool for the online study of aerosols with the ability to measure size-resolved chemical composition with a temporal resolution relevant to atmospheric processes. In SPMS, optical particle detection is used for the effective temporal alignment of an ablation laser pulse with the presence of a particle in the ion source, and it gives the option of aerodynamic sizing by measuring the offset of particle arrival times between two detection stages. The efficiency of the optical detection stage has a strong influence on the overall instrument performance. A custom detection laser system consisting of a high-powered fibre-coupled Nd:YAG solid-state laser with a collimated beam was implemented in the detection stage of a laser ablation aerosol particle time-of-flight (LAAP-TOF) single-particle mass spectrometer without major modifications to instrument geometry. The use of a collimated laser beam permitted the construction of a numerical model that predicts the effects of detection laser wavelength, output power, beam focussing characteristics, light collection angle, particle size, and refractive index on the effective detection radius (R) of the detection laser beam. We compare the model predictions with an ambient data set acquired during the Ice in Clouds Experiment – Dust (ICE-D) project. The new laser system resulted in an order-of-magnitude improvement in instrument sensitivity to spherical particles in the size range 500–800 nm compared to a focussed 405 nm laser diode system. The model demonstrates that the limit of detection in terms of particle size is determined by the scattering cross section (Csca) as predicted by Mie theory. In addition, if light is collected over a narrow collection angle, oscillations in the magnitude of Csca with respect to particle diameter result in a variation in R, resulting in large particle-size-dependent variation in detection efficiency across the particle transmission range. This detection bias is imposed on the aerodynamic size distributions measured by the instrument and accounts for some of the detection bias towards sea salt particles in the ambient data set.

Optical particle detection in liquid suspensions with a hybrid integrated microsystem

In this work, we present an optical microsystem for particle flow detection, based on hybrid integration and silicon micromachining. Sensing principle is light obscuration. We demonstrate the feasibility of integrating commercial components such as light sources (850nm near infrared Vertical-Cavity-Surface-Emitting Lasers VCSELs) and optics (an array of microlenses) into a silicon fabricated structure to create an optoelectronic package of reduced dimensions (14mm×12mm) and low power consumption (≈7.2mW) that satisfies optical requirements and provides four collimated laser beams with reduced diameter spots (minimum radius of 124μm measured as 1/e2 standard). Besides this microoptical system, the detection system is completed with a double linear array imaging sensor of 256 pixels, designed and fabricated in 0.35μm CMOS technology, and a microfluidic platform. The designed set-up allows the simultaneous optical detection of singly aligned microbeads flowing in liquid suspensions through several parallel microfluidic channels, which share the pitch of the laser emitting sources, i.e. 250μm. While the throughput of the system is increased up to 5000 particles/s thanks to the possibility of performing parallel measurements, the double array of the imaging sensor improves the detection process discarding false detected events. Experimental results prove that the system is able to detect and distinguish microparticles of several sizes in a mixed solution, with detection limit set at 10μm diameter. In conclusion, the fabricated microsystem is presented as a miniaturized and robust alternative to current optical microflow cytometers based on the use of optical fibre, and the complete system, including fluidics and imaging sensor stages, represents a portable solution packaged in less than 5cm3. These features make it an interesting choice to consider in the field of point-of-care biosensing applications.

Optical Particle Detection in Liquid Suspensions with a Hybrid Integrated Microsystem

A compact, robust and portable system for optical particle detection in liquid suspensions, achieved through the hybrid integration of commercial components, such as VCSELs and microlenses, in a silicon micromachined structure is presented. We demonstrate the feasibility of fabricating a device providing up to 4 collimated laser beams, with the ability of detecting and distinguishing microparticles of several diameters, even in mixed suspensions. This optical microsystem represents an alternative design for microflow cytometers based on optical fibres, and is aligned with the current tendency set by the Point-of-care devices.

Dual-core optofluidic chip for independent particle detection and tunable spectral filtering

We present the first integration of fluidically tunable filters with a separate particle detection channel on a single planar, optofluidic chip. Two optically connected, but fluidically isolated liquid-core antiresonant reflecting optical waveguide (ARROW) segments serve as analyte and spectral filter sections, respectively. Ultrasensitive detection of fluorescent nanobeads with high signal-to-noise ratio provided by a fluidically tuned excitation notch filter is demonstrated. In addition, reconfigurable filter response is demonstrated using both core index tuning and bulk liquid tuning. Notch filters with 43 dB rejection ratio and a record 90 nm tuning range are implemented by using different mixtures of ethylene glycol and water in the filter section. Moreover, absorber dyes and liquids with pH-dependent transmission in the filter channel provide additional spectral control independent of the waveguide response. Using both core index and pH control, independent filter tuning at multiple wavelengths is demonstrated for the first time. This extensive on-chip control over spectral filtering as one of the fundamental components of optical particle detection techniques offers significant advantages in terms of compactness, cost, and simplicity, and opens new opportunities for waveguide-based optofluidic analysis systems.

Detection of the Mass of Airborne Particles in an online Optical Sensor System by Correlation of Geometric and Inertial Filtering

We present a method combining inertial and geometric filtering to approximate the mass of particles for optical particle detection systems. The method consists of three measurement steps and is based on the difference of the filtering behavior of geometric and inertial filters based on particle size and particle density respectively. Our measurements show the feasibility using polystyrene latex particles with sizes 300/500/900 nm and silica particles with diameters 500 nm and 1000 nm.

Optical particle detection integrated in a dielectrophoretic lab-on-a-chip

The design and fabrication of a dielectrophoretic ‘lab-on-a-chip’ device for bioparticle processing and counting is presented. The device consists of a multi-layer travelling wave dielectrophoretic electrode array for manipulating particles and/or fluids, microchannels for delivering samples and optical fibres for counting particles and/or measuring their velocities. Single particles were detected optically using either light scattering or fluorescence emission. The technology described in this study is potentially applicable to a range of particulate diagnostic systems.

Time-of-flight mass spectrometry methods for real time analysis of individual aerosol particles

Recent instrumental developments allow for the analysis of single particles in real time. The techniques discussed in this review couple time-of-flight mass spectrometry for determining the chemical composition of individual aerosol particles with some form of optical particle detection. Applications to be discussed include the study of laboratory-generated particles and ambient particle sampling, including field studies aimed at measuring the temporal profiles of atmospheric particles.

Study of the ignition of single coal and char particles in a drop tube furnace by a probability method

A drop tube technique coupled with optical particle detection and three color pyrometry has been applied to study the ignition of single particles of a petroleum coke, a high volatile bituminous coal (Freyming-France) and their chars. The objective of the study was to measure the critical ignition temperatures and the ignition delays. This was performed in both cases in a pure oxygen atmosphere using five particle sizes: 100–125 μm, 125–160 μm, 160–200 μm, 200–250 μm and 250–315 μm. Forced ignition delays were measured only for chars. Results show, that critical ignition temperatures decrease with increasing char particle diameter and with decreasing coal or petroleum coke particle diameter. The Semenov's steady state thermal ignition theory was used to predict critical ignition temperatures. A transient heat balance equation was developed to predict ignition delays. The experimental results are correctly accounted for, except in the case of the smallest particles, for which the model over-predicts the ignition delays.

Film drop distributions from bubbles bursting in seawater

The liquid droplets produced from the breaking up of the film cap of oceanic bubbles have long been considered as constituting a significant fraction of the marine aerosol. The size and number distributions of these film drops are investigated for single bubbles that burst in seawater under laboratory conditions. Optical particle detection and counting techniques are used to size the droplets generated from bubbles varying in diameter from about 1 to 6 mm. Parallel measurements are also made using a laser holographic setup for bubbles up to about 10 mm in diameter. Taken together, a film drop size spectrum extending from 0.8 to 500 μm is covered. From these results, an experimental correlation between the number of film drops generated and the parent bubble diameter is proposed. Based on this correlation and published data concerning the number of jet drops produced per bubble, a crossover point for bubbles that produce predominantly either film drops or jet drops is located at a bubble diameter of about 1.8 mm. In other words, bubbles larger than this threshold diameter produce more film drops than jet drops, while smaller bubbles generate more jet drops. A couple of film drops as large as 500 μm for a 10 mm bubble are detected. Although these maximum sizes diminish with decreasing bubble diameter, they happen to be much larger than previously thought.