Corneal ulcers, typically caused by infection, are among the leading causes of vision loss and require prompt intervention. Without effective treatment, permanent vision impairment
[i] and more serious infections
[ii] can result. Rather than spending days culturing the pathogen to determine whether the infection is bacterial or fungal, antibiotics are typically applied as an empiric treatment
[iii]; as the incidence of fungal infections increases, however, complications are becoming more prevalent
[iv]. The two types of infection may instead be rapidly distinguished at point-of-care by means of a self-contained acoustic isolation and detection system, allowing doctors to immediately prescribe the appropriate remedy. The core of this system is a piezoelectric chip made from a material such as quartz or LiNbO
3 whose surface is functionalized with a chitin-binding lectin having a strong affinity for the cell walls of fungal pathogens. By electrically exciting this chip, Rayleigh waves lyse pathogen cells, mix the sample, and remove nonspecifically-bound materials
[v], purifying chitin and isolating it on the chip’s surface. The isolated analyte is then detected using a chitin-sensitive fluorescent probe. The detection limit may be further improved by means of metal-enhanced fluorescence using a thin layer of silver nanostructures formed by rapid thermal annealing that couple with the probe signal
[vi]. This technique has proven effective with other analytes at concentrations on the order of picograms per milliliter
[vii].
[i] McClintic, S. M., et al. "Improvement in corneal scarring following bacterial keratitis." Eye 27.3 (2013): 443-446.
[ii] Scott, Ingrid U., et al. "Endophthalmitis associated with microbial keratitis." Ophthalmology 103.11 (1996): 1864-1870.
[iii] Collier, Sarah A., et al. "Estimated burden of keratitis—United States, 2010." MMWR. Morbidity and mortality weekly report 63.45 (2014): 1027.
[iv] Tuberville, Audrey W., and Thomas O. Wood. "Corneal ulcers in corneal transplants." Current eye research 1.8 (1981): 479-485.
[v] Cular, Stefan, et al. "Removal of nonspecifically bound proteins on microarrays using surface acoustic waves." IEEE Sensors journal 8.3 (2008): 314-320.
[vi] Morrill, Samuel, Venkat Bhethanabotla, and Mandek Richardson. "Biomarker quantification at clinically relevant concentrations using metal enhanced fluorescence combined with surface acoustic waves." SENSORS, 2014 IEEE. IEEE, 2014.
[vii] Liu, Jun, Shuangming Li, and Venkat R. Bhethanabotla. "Integrating metal-enhanced fluorescence and surface acoustic waves for sensitive and rapid quantification of cancer biomarkers from real matrices." ACS sensors 3.1 (2018): 222-229.
