Aptasensors Based on Whispering Gallery Mode Resonators

Abstract

In this paper, we review the literature on optical evanescent field sensing in resonant cavities where aptamers are used as biochemical receptors. The combined advantages of highly sensitive whispering gallery mode resonator (WGMR)-based transducers, and of the unique properties of aptamers make this approach extremely interesting in the medical field, where there is a particularly high need for devices able to provide real time diagnosis for cancer, infectious diseases, or strokes. However, despite the superior performances of aptamers compared to antibodies and WGMR to other evanescent sensors, there is not much literature combining both types of receptors and transducers. Up to now, the WGMR that have been used are silica microspheres and silicon oxynitride (SiON) ring resonators.

Keywords: aptamers; integrated rings; microspheres; optical sensors; whispering gallery mode resonators.

Figure 1

(a) Schematic of the microsphere and fluidic cell (side view); (b) top view of the fiber prism with a microsphere. Reprinted with permission from [7] © 2006 MDPI.

Figure 2

A schematic diagram of the experimental arrangement. Reprinted with permission from [24] © 2012 MDPI.

Figure 3

A schematic diagram of the microring based biosensor. Left: the input light is split into the four ring resonators using directional couplers with a gap of 600 nm. Right: zoomed in image of the ring resonator structure. The gap and coupling length between the bus waveguide and the resonator are 600 nm and 35 μm, respectively. The radius of the resonators is 100 μm. Reprinted with permission from [25] © 2015 Elsevier.

Figure 4

Control experiments: (a) whispering gallery mode resonator (WGMR) response of a Thrombin Binding Aptamer (TBA)-15 sensing surface for 0.3 mg/mL Bovine Serum Albumin (BSA) injected into the flow cell and (b) sensorgram using a non sense aptamer sensing surface for 0.3 mg/mL thrombin.

Figure 5

(a) WGMR response with TBA-15 modified resonator following the addition of thrombin in buffer (b) Sensorgram of thrombin binding to a WGMR immobilized with TBA-15 in 1:10 non-filtered human serum, following the addition of thrombin.

Figure 6

Sensorgram of thrombin binding to a regenerated WGMR immobilized with TBA-15, following the addition of thrombin (two identical additions of 5 μL of 0.1 mg/mL of thrombin).

Figure 7

(left) Sensorgram for three different concentrations of alflatoxin M1 (AFM1). The high step-like response is due to the refractive index mismatch produced by the small content of Dimethyl sulfoxide (DMSO) in the solution; (right) Specific binding sensorgrams obtained from the curves in (left) by subtracting the bulk shift induced by the DMSO content. The dashed curves are exponential fittings for the evaluation of the rate constants and of the initial slopes [27]. Reprinted with permission from [9] © 2015 MDPI.