Field-portableLensfree Reflection Holographic Microscopy
Myungjun Lee* and Aydogan Ozcan*,†
*Electrical Engineering Department, † California NanoSystems Institute (CNSI), University of California at Los Angeles, CA 90095-1594
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Summary: We present a compact, cost-effective and lensfree reflection holographic on-chip microscope that can digitally image densebiological tissues (such as histopathology slides),providing a lateral resolution of ~2µm over the wide field-of-view (FOV) ~ 10mm2.
Digital holographic microscopy (DHM) has recently attracted significant interest for its ability to retrieve both amplitude and phase information of optical waves that are either transmitted through the sample or reflected by it [1]. In particular, various lensfree on-chip microscopy techniques have been recently demonstrated for the specific purpose of conducting microscopy in resource limited settings using compact and cost-effective imaging architectures [2].However, in-line transmission geometry of these lensfree holographic microscopes has a limitation to image dense or thick objects like biological tissues. In order to overcome this limitation, here we demonstrate a lensfree on-chip reflection microscope that can image dense objects such as histopathology slides, providing ~2µm resolution overa large FOV of ~ 10mm2.
(a) (b) (c) (d)
Fig. 1. a) Experimental configuration of our reflection-mode lensfree on-chip microscope. b) Lensfree reflection mode image of a resolution target. c) Lensfree reflection mode image of a histopathology slide corresponding to skin tissue. d) Conventional reflection microscope image (4X objective lens - 0.1 numerical aperture) that is provided for comparison images.
Figure. 1(a) shows the schematic diagram of ourlensfree reflection mode microscope that is based on off-axis digital holography utilizing a Michelson interferometer geometry.The light emitted from a 20mW green laser diode (LD) ata wavelength of 531nm is passedthrough a 3µm pin-hole (PH),which thenilluminates a beam cube (BC) to split into two beams.The first beam is directed toward a sample specimen andis then reflected back, while the other is directed to a reference mirror (Fig. 1). These reflecting wavefronts with a slight anglein between interfere at the CMOS sensor-chip, creating an off-axis reflection hologramof the specimens. This recorded hologram is digitally filtered in the Fourier domain to remove the zeroth order term, twin image artifact and multi-reflection noise terms. After this filtering operation, both the phase and amplitude images of the specimenscan be rapidly reconstructed over a large FOV of ~10 mm2. To validate the performance of our lensfree reflection DHM, we first imaged a US air-force resolution target, as shown in Fig. 1 (b), achieving alateral resolution of <2 µm.As illustrated in Fig. 1(c) we also imaged with the same lensfree reflection microscope a histopathology slide corresponding to skin tissue. For comparison purposes, Fig. 1(d) also showsthe imageof the same specimen taken with a conventional reflection mode optical microscope(4X-objective-lens, NA=0.1), which agrees well with our lensfree microscope image. We believe that this compact, cost-effective and lensfree reflection mode microscopyplatform, providing ~2 µm lateral resolution over a wide FOV of~10mm2, could be quite useful for field-use in resource limited environments.
[1] Myung K. Kim, "Principles and techniques of digital holographic microscopy", SPIE Rev 1, 018005 (May 14, 2010); doi:10.1117/6.0000006 [2]Mudanyali, O. et al. Compact, light-weight and cost-effective microscope based on lensless incoherent holography for telemedicine applications. Lab Chip 10, 1417 (2010).