Abstract
Early and efficient disease diagnosis with low-cost point-of-care devices is gaining importance for personalized medicine and public health protection. Within this context, waveguide-(WG)-based optical biosensors on the silicon-nitride (Si3N4) platform represent a particularly promising option, offering highly sensitive detection of indicative biomarkers in multiplexed sensor arrays operated by light in the visible-wavelength range. However, while passive Si3N4-based photonic circuits lend themselves to highly scalable mass production, the integration of low-cost light sources remains a challenge. In this paper, we demonstrate optical biosensors that combine Si3N4 sensor circuits with hybrid on-chip organic lasers. These Si3N4-organic hybrid (SiNOH) lasers rely on a dye-doped cladding material that are deposited on top of a passive WG and that are optically pumped by an external light source. Fabrication of the devices is simple: The underlying Si3N4 WGs are structured in a single lithography step, and the organic gain medium is subsequently applied by dispensing, spin-coating, or ink-jet printing processes. A highly parallel read-out of the optical sensor signals is accomplished with a simple camera. In our proof-of-concept experiment, we demonstrate the viability of the approach by detecting different concentrations of fibrinogen in phosphate-buffered saline solutions with a sensor-length (L-)-related sensitivity of S/L = 0.16 rad nM−1 mm−1. To our knowledge, this is the first demonstration of an integrated optical circuit driven by a co-integrated low-cost organic light source. We expect that the versatility of the device concept, the simple operation principle, and the compatibility with cost-efficient mass production will make the concept a highly attractive option for applications in biophotonics and point-of-care diagnostics.
Highlights
Integrated sensors based on optical waveguides (WGs) exhibit an enormous application potential in biophotonics and medical diagnostics, especially when it comes to multiplexed, highly sensitive detection of a wide variety of target molecules[1,2]
The Si3N4-organic hybrid (SiNOH) lasers are pumped from the top by an external light source with a large spot size such that high-precision alignment of the chip with respect to the pump beam is not needed
The generated laser light is coupled with a Si3N4 single-mode WG and guided to an array of on-chip sensors
Summary
Integrated sensors based on optical waveguides (WGs) exhibit an enormous application potential in biophotonics and medical diagnostics, especially when it comes to multiplexed, highly sensitive detection of a wide variety of target molecules[1,2]. With a few exceptions in the mid-infrared wavelength range[14], biosensors on the Si3N4 integration platform remain limited to mainly passive circuits and usually rely on external light sources coupled to the chip[5,15,16,17] This requires delicate fibre-chip coupling schemes that are subject to stringent mechanical tolerances, which conflicts with the demand for technically simple low-cost sensor systems for point-of-care diagnostics. Cointegration of sensor circuits with on-chip lasers might represent an alternative, but all demonstrations have so far been limited to NIR sources that are first realized on a separate substrate and that are flip-chip mounted onto passive Si3N4 PICs in a dedicated assembly step[18] This involves serial assembly processes and mitigates most of the scalability advantages of highly parallel wafer-level mass fabrication. It is uncertain whether high-precision assembly of discrete laser dies could comply with the stringent cost limitations of disposable biosensors
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