title: Ultrasensitive interferometric on-chip microscopy of transparent objects.
abstract: Light microscopes can detect objects through several physical processes, such as scattering, absorption, and reflection. In transparent objects, these mechanisms are often too weak, and interference effects are more suitable to observe the tiny refractive index variations that produce phase shifts. We propose an on-chip microscope design that exploits birefringence in an unconventional geometry. It makes use of two sheared and quasi-overlapped illuminating beams experiencing relative phase shifts when going through the object, and a complementary metal-oxide-semiconductor image sensor array to record the resulting interference pattern. Unlike conventional microscopes, the beams are unfocused, leading to a very large field of view (20 mm(2)) and detection volume (more than 0.5 cm(3)), at the expense of lateral resolution. The high axial sensitivity (<1 nm) achieved using a novel phase-shifting interferometric operation makes the proposed device ideal for examining transparent substrates and reading microarrays of biomarkers. This is demonstrated by detecting nanometer-thick surface modulations on glass and single and double protein layers.
authors.affiliation: ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.
authors.forename: Roland A
authors.identifier: 0000-0002-7246-0597
authors.initials: RA
authors.lastname: Terborg
authors.affiliation: ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.
authors.forename: Josselin
authors.identifier: 0000-0002-3352-0198
authors.initials: J
authors.lastname: Pello
authors.affiliation: ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.
authors.forename: Ilaria
authors.identifier: 0000-0001-5322-839X
authors.initials: I
authors.lastname: Mannelli
authors.affiliation: ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.; Department of Signal Theory and Communications, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain.
authors.forename: Juan P
authors.initials: JP
authors.lastname: Torres
authors.affiliation: ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain.; ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain.
authors.forename: Valerio
authors.identifier: 0000-0002-6425-9332
authors.initials: V
authors.lastname: Pruneri
mesh_terms: D004867:Equipment Design; D008857:Microscopy, Interference / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D008858:Microscopy, Phase-Contrast; D057054:Molecular Imaging / Q000379:methods; D012680:Sensitivity and Specificity
keywords: digital interference contrast microscopy; high-throughput biodetection; interferometry; lens-free imaging; on-chip sensing