Label-free detection with the liquid core optical ring resonator sensing platform

Abstract

Optical label-free detection prevents the cost and complexity of fluorescence and radio labeling while providing accurate quantitative and kinetic results. We have developed a new optical label-free sensor called the liquid core optical ring resonator (LCORR). The LCORR integrates optical ring resonator sensors into the microfluidic delivery system by using glass capillaries with a thin wall. The LCORR is capable of performing refractive index detection on liquid samples, as well as bio/chemical analyte detection down to detection limits on the scale of pg/mm2 on a sensing surface.

Figure 1

LCORR sensing platform. (A) The ring resonator is defined in the cross-section of the LCORR capillary, and is excited by evanescent coupling from a fiber taper or waveguide; (B) An evanescent field at the inner surface interacts with the sample; (C) Detection of analytes causes a spectral shift in the resonant wavelength; the spectral position of the resonant wavelength over time forms the sensing signal.

Figure 2

The process for conducting a bio/chemical molecule detection experiment using the LCORR sensing platform.

Figure 3

(A) Diagram of LCORR drawing setup (reproduced from ref.8 with permission from SPIE). (B) Photo of a constructed setup to draw LCORRs.

Figure 4

LCORR capillary after pulling from a preform.

Figure 5

(A) Setup for pulling fiber tapers. (B) Photo of a constructed setup to pull tapers.

Figure 6

(A) Sketch and (B) photo of a fiber taper anchored onto a portable mount.

Figure 7

LCORR sensing platform experimental setup (reproduced from ref.7 with permission from SPIE).

Figure 8

(A) Temperature control setup for the LCORR sensor. (B) Photo of a taper and LCORR mounted on the temperature control setup. A white line is drawn along the taper so that it can be visualized.

Figure 9

(A) Sketch an (B) photo of an LCORR with attached tubing, mounted on a portable mount.

Figure 10

The observed WGM shift in response to a 10% ethanol solution replacing water inside an LCORR with a sensitivity of 315 pm/RIU.

Figure 11

The measured refractive index sensitivity for an exemplary LCORR. Data is recorded for ethanol solutions of 10%, 20%, 30%, 40%, and 50%. The values are the result of an average across at least 6 observed WGM shifts. The slope of the linear fit is the refractive index sensitivity.

Figure 12

Sensorgram showing the binding of BSA molecules at the inner surface of the LCORR capillary. The BSA concentration is 1 mg/ml.

Figure 13

Sensorgram showing the proteolytic activity of trypsin acting to remove BSA bound at the inner surface of the LCORR capillary. The trypsin concentration is 10 μg/ml.

Figure 14

Surface chemistry for immobilizing oligo probes to the LCORR surface.

Figure 15

Exemplary sensorgram for 3-APS functionalization, 25 base-pair oligo probe immobilization, and sample detection (25 base pair DNA sequence). In this case, all steps, including the 3APS deposition, were performed in 3X-SSC buffer. Therefore, there are no WGM spectral shifts due to buffer changes.