Lensfree sensing on a microfluidic chip using plasmonic nanoapertures

Abstract

We demonstrate lensfree on-chip sensing within a microfluidic channel using plasmonic nanoapertures that are illuminated by a partially coherent quasimonochromatic source. In this approach, lensfree diffraction patterns of metallic nanoapertures located at the bottom of a microfluidic channel are recorded using an optoelectronic sensor-array. These lensfree diffraction patterns can then be rapidly processed, using phase recovery techniques, to back propagate the optical fields to an arbitrary depth, creating digitally focused complex transmission patterns. Cross correlation of these patterns enables lensfree on-chip sensing of the local refractive index surrounding the near-field of the plasmonic nanoapertures. Based on this principle, we experimentally demonstrate lensfree sensing of refractive index changes as small as ∼2×10(-3). This on-chip sensing approach could be quite useful for development of label-free microarray technologies by multiplexing thousands of plasmonic structures on the same microfluidic chip, which can significantly increase the throughput of sensing.

Handheld high-throughput plasmonic biosensor using computational on-chip imaging

“…However, we should also note that quantitative sensing information of the binding events could also be extracted from only the diffraction patterns of the same nanoapertures in case the physical separation between neighboring aperture regions is large, minimizing the intensity overlap at the detector/sampling plane. 66 Using this phase recovery approach procedure, we can reduce the distance between individual sensory pixels even down to 2 mm. 66 A single sensor with a size of 10 mm310 mm, consisting of more than 200 nanoholes (hole diameter5200 nm and array period 600 nm) should result in sufficient transmitted signal to be captured by the CMOS imager.…”

“…66 Using this phase recovery approach procedure, we can reduce the distance between individual sensory pixels even down to 2 mm. 66 A single sensor with a size of 10 mm310 mm, consisting of more than 200 nanoholes (hole diameter5200 nm and array period 600 nm) should result in sufficient transmitted signal to be captured by the CMOS imager. 84 Based on these numbers, employing a CMOS imager with an active area of 5.7 mm34.3 mm, we could image 170 000 sensor pixels all in parallel, which is highly promising for high-throughput applications.…”

“…In this on-chip microscopy platform, computational holographic reconstruction and phase recovery methods are used to partially eliminate diffraction effects, providing higher resolution microscopic images across very large imaging areas, e.g., .20-30 mm 2 using off-the-shelf CMOS (Complementary Metal-Oxide-Semiconductor) imager chips. 65,66 Together with the improvements provided by unique sample preparation and self-assembly techniques, lens-free on-chip imaging can even detect single viruses and sub-100 nm particles 67,68 across a wide field of view, e.g., .20 mm 2 and provides a highthroughput nano-imaging platform.…”

Flexible Plasmonic Sensors

“…Additionally, engineered sub-wavelength plasmonic nanostructures which support strong, concentrated near field modes and less stringent momentum matching requirements for resonant coupling have been showcased as powerful substrates for both LSRP and SERS [13]–[15]. These plasmonic nano-structures have traditionally been fabricated through standard semiconductor fabrication techniques, which limited such plasmonic designs to mainly rigid Si or SiO 2 substrates [17]. Moreover, these fabrication techniques are generally costly, requiring a clean room with expensive, dedicated equipment and are often inherently low-throughput, by and large limiting their fabrication and use to resource rich laboratories [14], [18]–[20].…”

Synthetic aperture-based on-chip microscopy

“…In contrast, recent advances in digital components and computational techniques have enabled powerful imaging methods, [1][2][3][4][5][6][7][8][9][10] and when these are combined with state-of-the-art image sensor technology, it has made lenses unnecessary in certain microscopic imaging tasks. [11][12][13][14][15][16][17] For example, by taking advantage of image sensor chips with large mega-pixels, small pixel pitch and low cost, lensfree holographic on-chip microscopy provides unique opportunities for achieving ultra-large SBP within a cost-effective and compact imaging design. [18][19][20] Using source-shifting-based pixel super-resolution techniques, 18,21 lensfree on-chip imaging achieves submicrometer resolution over a wide FOV of 20-30 mm 2 , providing gigapixel throughput with a simple, compact and unit-magnification design.…”