Nanophotonics-based Intraocular Pressure (IOP) Sensor with Remote Optical Readout

Abstract

 

Purpose

 

To develop a miniaturized nanophotnonics-based implantable device for frequent, automated remote monitoring of IOP.

 

Methods

 

The basic nanophotonics IOP sensor consists of a sealed cylindrical chamber, with gold nanodot arrays on flexible membranes forming the top & bottom chamber surfaces (Fig. 1 A). When interrogated with light, the reflected signal from the device shows maximal reflectance dips at specific wavelengths, and is the spectral signature of a unique gap size between nanodot arrays. Within the anterior chamber, the nanodot membranes deform as the ambient pressure, i.e. IOP rises, causing the gap between arrays to decrease (Fig. 1 B). This gap narrowing causes the reflectance spectrum to shift (Fig. 1 C, D), and is detected remotely via a spectrometer.

 

Results

 

Proof of concept devices were fabricated consisting of two thin rigid glass substrates containing gold nanodot arrays, separated from each other by ~6 μm-thick photoresist (Fig. 2 A). 5 devices with gaps of 6.32, 6.38, 6.45, 6.51, and 6.60 μm were interrogated and the reflected signal analyzed using a spectrometer. The reflectance spectra showed a systematic shift in the reflectance dip maxima with increasing gap separation (Fig. 2 B), in agreement with predictions from simulation. Prototypes were also implanted into rabbit eyes ex vivo (Fig. 2 C, D). A reflectance spectrum with identifiable reflectance dips was detected remotely at 7 mm from the nanodot arrays (Fig. 2 F).

 

Conclusions

 

A nanophotonics-based method of IOP sensing is in principle viable. Advantages of this approach include potential miniaturization to obtain 25-50 μm devices and remote sensing using light ultimately at a distance of 5 cm or larger.

 

 

Fig 1. Schematic and operating principle of IOP sensor A) Cylinder-shaped chamber structure. B) Deformable membranes allow gap size variation with pressure. C) Reflectance spectrum with characteristic dips D) Reflectance dips shift to shorter wavelengths as gap narrows.

 

 

Fig 2. A) Schematic of rigid coverslip prototypes with nanodot arrays. B) As the gap size decreases, the resonance systematically shifted to a shorter wavelength. C) Nanophotonics sensor in rabbit anterior chamber. D) Higher mag. Arrow shows 50 X 50 μm2 sensor array. Scale = 1 mm. E) Reflectance spectrum from sensor in saline. Arrows show reflectance dips. F) Spectrum from same sensor in anterior chamber.

 

Keywords: 568 intraocular pressure • 607 nanotechnology