Nano-optofluidic Detection

We are developing an optical detection scheme for the real-time and label-free detection and recognition of single nanoparticles, such as viruses, larger proteins, and contaminants. Nanoparticles are detected in real-time (no immobilization), without artificial labels, and with single particle sensitivity (one particle at a time). The reliable detection, sizing, and sorting of nanoparticles is important for biosensing, environmental monitoring, and quality control.

The detection method, illustrated in the figure above, makes use of nanofluidic channels in combination with optical interferometry. Elastically scattered light from single nanoparticles traversing a stationary laser focus is detected with a differential heterodyne interferometer and the resulting signal allows single nanoparticles to be characterized individually. Heterodyne or dark-field detection eliminates phase variations due to different particle trajectories, thus improving the recognition accuracy as compared to standard optical interferometry.

The figure above shows a magnified image of nanofluidic channels fabricated into a borosilicate glass wafer. Nanoparticles are transported from a bottom reservoir through the nanochannels (cross section 500 nm, length 15 to a top reservoir by either electroosmosis or pressure-driven flow. One of the nanochannels is selected and a laser focus is placed at its center to detect the passage of individual nanoparticles.

Individual particles traversing the laser focus render a characteristic signal (see figure below), from which we can extract particle size and material properties. The uncertainty in particle size is determined by laser shot noise and instrument stability. The current size uncertainty is 0.3nm (figure below, right).

So far, the detection scheme has been applied to a variety of targets, including viruses (Influenza, Parainfluenza, Baculovirus, Vaccinia, HIV, Sindbis), phages, metal and semiconducting nanoparticles, and carbon particles. A size histogram of individually detected phages is shown in the figure below along with an electron micrograph of phage particles. Different viruses can be distinguished based on their size distributions.

An important application area of the detection method is contamination control of processing fluids, such as etchants or immersion fluids used in the semiconductor industry. Other application areas are the quality control of drinking water and trace detection of hazardous agents.


Related Publications:

[1] A. Mitra, F. Ignatovich and L. Novotny, ”Nanofluidic preconcentration and detection of nanoparticles,” J. Appl. Phys. 112, 014304 (2012).

[2] O. Block, A. Mitra, L. Novotny and C. Dykes, ”A rapid label-free method for quantitation of human immunodeficiency virus Type-1 particles by nanospectroscopy,” J. Virol. Meth. 182, 70-75 (2012).

[3] A. Mitra, F. Ignatovich and L. Novotny, ”Real-time optical detection of single viruses and phage based on dark-field interferometry,” Biosensensors and Bioelectronics 31, 499-504 (2012).

[4] S. Person, B. Deutsch, A. Mitra, and L. Novotny,, ”Material-specific detection and classification of single nanoparticles,” Nano Lett. 11, 257-261 (2011).

[5] A. Mitra, B. Deutsch, F. Ignatovich, and L. Novotny, ”Nano-optofluidic detection of single viruses and nanoparticles,” ACS Nano 4, 1305-1312 (2010).

[6] F. V. Ignatovich and L. Novotny, “Optical detection of single particles and viruses,” IEEE J. of Selected Topics in Quant. Electronics 12, 1292-1300 (2006).

[7] F. V. Ignatovich and L. Novotny, “Real-time and background-free detection of nanoscale particles,” Phys. Rev. Lett. 96, 013901 (2006).