Optical sensing devices which use various sensing principles are known. A good background description on the state of the art is provided in U.S. Pat. No. 7,447,391 to Asher Peled et al., as well as in “Novel monolithic amplifiers, lasers and intra-cavity interferometric sensors based on Nd-doped sol-gel”, PhD thesis, Asher Peled, Tel Aviv University, submitted November 2008, to be published 2009 (hereinafter “Peled 2009”), both of which are incorporated herein by reference in their entirety. In particular, interferometric optical sensors in various configurations, such as Mach Zehnder interferometers (MZI) and Young interferometers are known to have the best reported sensitivities.
U.S. Pat. No. 7,447,391 discloses biological and chemical optical sensing devices comprising at least one planar resonator structure included in a sol-gel light emitting (or simply “emitting”) waveguide and at least one biological or chemical probe bound to at least a part of the resonator structure, the probe operative to bind specifically and selectively to a respective target substance, whereby the specific and selective binding results in a parameter change in light emitted from the waveguide. The sensed parameter may be a spectral change, e.g. a spectral shift, or a Q-factor change which is encoded in the emitted optical signal and which may be read remotely by an optical reader. In some embodiments, the resonator structure is linear and the waveguide is “active” or “light-emitting’, The “active” or “light-emitting’ terminology reflects the incorporation of at least one light emitting material (e.g. photluminescent—“PL” or laser material) in the sol-gel and emission of light generated from this light-emitting material. In some embodiments, this material can be remotely pumped by a remote optical source and excited to emit the light which is outcoupled from the device to a remote detector (e.g. spectrometer).
Amplifiers and lasers based on on Nd-doped sol-gel light-emitting structures are described respectively in A. Peled et al., “Neodimium doped sol-gel tapered waveguide amplifier”, Applied. Physics Letters, Vol. 90, 161125, 2007 (hereinafter “Peled 2007”) and in A. Peled et al., “A monolithic solid-state laser realized by neodymium doped silica-hafnia sol-gel tapered rib waveguide”, Applied Physics Letters Vol. 92, 221104, 2008 (hereinafter “Peled 2008”), both incorporated herein by reference in their entirety.
Light-emitting (for example sol-gel) biosensors such as described above are robust and immune to temporal variations (instabilities) of the optical source power and to the efficiency of light coupling into and out of the sensor chip. This immunity is achieved since these sensors encode the measured parameter in their emission spectrum rather than in the emission intensity. In addition, these sensors can in principle be implantable, because both the pumping and the spectral interrogation of their emitted light are performed remotely. However, their sensitivity is expected to be less than that of interferometric biosensors.
Y-branch waveguide lasers are known, see e.g. N. A. Sanford et al., Optics Letters, Vol. 16, n. 15(1), p. 1168-70, 1991, as well as Peled 2009, page 19 and references therein. The device of Sanford et al. has an “imbalanced” geometry in which the branch segments are mismatched in length by 2.4%. Stanford's device uses external reflectors attached to the structure to achieve resonance and lasing (i.e. his waveguide laser is not monolithic). Prior art Y-branch waveguide lasers are not known to be designed and used for sensing in general and biosensing or chemosensing in particular. When Y-branch waveguide structures were used for biosensing, as in T. J. Wang et al., Biosensors and Bioelectronics, vol. 22, pp. 1441-1446, 2007, they were not lasers but passive devices which do not emit internally generated light.
Immunoassays using optical sensors are normally done in “wet” mode, via a flow cell in which a sample liquid flows on the sensor surface. This enables to measure the chemical kinetics of interactions and to evaluate kinetic rate constants, as well as to follow interactions during changes introduced to the sample liquid. Nevertheless, wet immunoassays have some serious drawbacks. For example, changes in temperature of the flowing sample liquid strongly impact its refraction index and disrupt the optical reading. The reading is also disturbed by turbulence in the flow. These issues are solved by a sophisticated flow system with a delicate and tight control of the flowing sample liquid temperature. This complexity significantly raises the cost of wet optical immunoassay systems, rendering them inappropriate for point-of-care applications.
There is thus a recognized need for, and it would be advantageous to have, inexpensive and disposable sensors which combine the benefits of the robust spectral interrogation of light-emitting sensors as described above with the sensitivity of interferometric sensors. Moreover, it would be advantageous to use such sensors in dry biological immunoassays (where they serve as biosensors).