Purdue University innovators are taking cues from the spider to develop better 3D photodetectors for biomedical imaging.

Inspired by the repeating architecture patterns of a spider web, the team demonstrated a resilient, dome-shaped photodetector array that detects both direction and intensity of incident light at the same time, like the compound-eye vision system of arthropods such as insects and crustaceans.

"We employed the unique fractal design of a spider web for the development of deformable and reliable electronics that can seamlessly interface with any 3D curvilinear surface," said Chi Hwan Lee, a Purdue assistant professor of biomedical engineering and mechanical engineering.

Such 3D optoelectronic architectures are especially valuable for photodetection systems that require larger fields of view, wider angles of vision, and higher sensitivity to motion.

The work is published in the online journal Advanced Materials .

Why a Spider Web?

Spider webs are well known to provide excellent mechanical adaptability and damage-tolerance against various mechanical loads, even in a storm.

The unique structural property of Lee and his team's fractal web design protects the device by effectively tolerating various external loads.

Inspired by the natural architecture, Lee and his team's optical arrangement distributes externally induced stress throughout the threads, according to the effective ratio of spiral and radial dimensions.

The hemispherical photodetector array contains an organic‐dye‐sensitized material: a graphene hybrid composite. The device is first fabricated on a planar silicon wafer at the microscale and then transferred to transparent hemispherical domes with different curvatures in a deterministic manner.

The "web" provides greater extensibility to better dissipate force under stretching. Additionally, the design tolerates minor cuts of the threads while maintaining overall strength and function of the entire web architecture.

In a short, edited Q&A with Tech Briefs below, Prof. Lee explains how the spider structure can lead to a new kind of deformable electronics.

Tech Briefs: Why is it valuable for an optoelectronic architecture to have a web-like design?

Prof. Chi Hwan Lee: Optoelectronic materials and devices deployed across curvilinear surfaces offer qualitatively expanded levels of functionality enabling a large field of view with no aberration, which resembles the compound-eye vision system of arthropods. These 3D optoelectronic architectures are particularly attractive for photodetection systems that require a large field of view and wide-angle antireflection. To engineer a compound eye-mimicking system, the most promising procedures involve direct printing of photosensitive pixels on curved or hemispherical surfaces in a carefully-aligned manner.

Tech Briefs: What is the most exciting application or possibility with this type of design?

Prof. Lee: These efforts pave the way for realizing various 3D forms of photodetectors, but progress in this area is impeded by the complexity of assembling optoelectronic devices and components onto non-planar surfaces at the microscale and matching the shape of photodetector array with the fixed hemispherical curvature.

To tackle the challenge, we employed the structural architecture, or fractal design, of a spider web found in nature which is capable of efficiently resisting various mechanical loads from environments. The fractal web design that exhibits a repeating pattern on all scales provides unique capabilities to (1) distribute externally-induced stress throughout the threads according to the effective ratio of spiral and radial dimensions; (2) provide greater extensibility to better dissipate force under stretching; and (3) tolerate minor cuts of the threads while maintaining overall strength and function of the entire web architecture.

Tech Briefs: How well does your array work?

Prof. Lee: Our 3D photodetector provides not only the advanced optoelectronic functionality in detecting both direction and intensity of incident light but also superior photoresponsivity, compared to other similar counterparts, through the use of a novel organic dye-sensitized graphene hybrid composite as a flexible and effective photoactive component.

The resulting 3D optoelectronic architectures are particularly attractive for photodetection systems that require a large field of view and wide-angle antireflection, which will be useful for many biomedical and military imaging purposes.

Tech Briefs: What’s next with your research?

Prof. Lee: Our work establishes a platform technology that can integrate a fractal web design with system-level hemispherical electronics and sensors, thereby offering several excellent mechanical adaptability and damage-tolerance against various mechanical loads (like spider webs do). The assembly technique presented in this work enables deploying 2D deformable electronics in 3D architectures, which may foreshadow new opportunities to better advance the field of 3D electronic and optoelectronic devices. The U.S. patent is being filed through OTC, and we are seeking partners and also looking to license the technology.

This work is supported by the National Science Foundation (NSF; CMMI-1928784) and the Air Force Research Laboratory (AFRL; S-114-054-002), in collaboration with Prof. Muhammad Ashraf Alam’s Lab in ECE at Purdue. The work is published in Advanced Materials .

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