This PDF file contains the front matter associated with SPIE Proceedings Volume 11810, including the Title Page, Copyright information, and Table of Contents.

Conjugated polymers provide a unique toolbox for establishing electrical communication with biological systems. In the first half of this talk, I will introduce the type of conjugated polymers used at the biological interface. I will then show how we designed organic electrochemical transistors (OECTs) for protein detection at the physical limit and challenged them using COVID-19 patient samples, marking a considerable step toward biochemical sensing. I will discuss that advances in bioelectronic device designs do not appear by chance but stem from in-depth investigations of the active materials' transport properties, understanding of device operation, and enhancing materials’ compatibility with biorecognition units.

Cephalopods (e.g., squids, octopuses, and cuttlefish) have captivated the imagination of both the general public and scientists alike due to their sophisticated nervous systems, complex behavioral patterns, and visually stunning camouflage displays. Given their unique capabilities and characteristics, it is not surprising that these marine invertebrates have emerged as exciting models for novel adaptive optical and photonic materials. Within this context, our laboratory has developed various cephalopod-derived and cephalopod-inspired systems with dynamic functionalities within the visible and infrared regions of the electromagnetic spectrum. Our findings hold implications for next-generation adaptive camouflage devices and biomedical imaging technologies.

The change in optical properties of an organic semiconductors upon forming adducts with inexpensive small molecules is attractive in organic electronics. We focus on the adducts of conjugated molecules and Lewis acids (CM-LA), formed by the partial electron transfer from a CM containing a Lewis basic site to an LA such as BF3 and B(C6F5)3. The resulting adducts showed intriguing optoelectronic properties, including a red-shift in optical transitions and an increase in charge carrier density compared to the parent conjugated molecules. In this work, we combine electronic structure modelling and machine learning (ML) to quantify, analyze and predict the electron transfers and red-shifts of the adducts from chemical structures. For ML model, we utilize DFT-calculated electron transfers and redshifts and molecular descriptors readily calculated from molecular structures. Our work can help researchers in other fields in predicting fundamental properties from molecular structures.

The talk describes a bio-inspired approach to design and prepare proton conducting materials based on self-assembling short protein sequences (peptides). The effect of amino-acid side-chain and backbone conformation on proton conductivity of the peptide fibrils will be discussed. We will show that the rational design of peptides can lead to fabrication of novel type of environmentally friendly, high performance, self-assembling, proton conducting materials.

The applications of functional nanomaterials towards biological interfacing continue to emerge in various fields, such as in drug delivery and tissue engineering. While the rational control of surface chemistry and mechanical properties have been achieved for several of these biocompatible systems, these biomaterials are rarely synthesized with optical and electronic functionalities that could be beneficial for controlling the behavior of excitable cells for biosensing applications. In this talk, the development of self-assembling peptide materials appended with organic electronic units will be discussed. These materials can facilitate photoinduced energy transfer under aqueous environments. Semiconducting peptide monomers that can self-assemble as aligned hydrogels are successfully built according to design principles that allowed for directed photonic energy transport, sequential electron transport in a multicomponent system, and transmission or equilibration of voltage or current when incorporated in a transistor device. These soft scaffolding materials, with tunable molecular to macroscale properties, offer a unique tissue engineering platform that can locally and synergistically deliver electronic, topographical, and biochemical cues to cells. This presentation will also discuss the future applications of optoelectronically-active peptide assemblies as tools for controlling cellular processes and probing biophysical phenomena, such as action potential propagation, mechanotransduction, and drug/toxicant permeation across tissues.

Nature uses proteins for a variety of functions, and among all others, their ability to form high-hierarchical structures as well as to mediate charges. We are inspired by these functions of proteins in nature and utilize proteins for the formation of large-scale conductive materials. We report here on a new family of conductive biopolymers using only sustainable and abundant proteins. We show that our new biopolymers have superior mechanical properties and ionic conductivity, which is due to their high water uptake and the presence of oxo-amino-acids. We further show that our biopolymers can be easily functionalized in different ways, thus enhancing their ionic conductivity, enabling electron conduction, and introducing optoelectronic properties. We currently use our polymers for making new biosensors. These polymers are environmentally friendly, biodegradable, biocompatible, and low-cost, and we foresee their integration in numerous applications from biomedical to energy applications

Photosynthetic microorganisms and their Reaction Center (RC) photoenzymes can be used as active materials for bio-optoelectronic applications. Here we report approaches to interface RC molecules extracted from Rhodobacter sphaeroides with electrodes aiming to integrate the RC in electronic and electrochemical devices. Covalent binding with molecular semiconductors or supramolecular organization based on selective interactions have been explored. Alternatively, entrapment of the RC in biocompatible polymers is a convenient approach. These soft structures include polydopamine-based films or polydopamine/ethylenediamine nanoparticles capable of confining and protecting the RC, while improving RC-electrode charge transfer. We also describe the use of these polymers to address living photosynthetic bacterial cells on electrodes.

The ultraviolet (UV) index is an international standard measure of the strength of solar ultraviolet radiation on the earth's surface at a specific place and time. Solar radiation with a high UV index can produce damage to the skin and eye (photoaging and photokeratitis). The levels of UV radiation are commonly detected using silicon-based optoelectronic sensors, which can be expensive. Here we propose a way to measure the UV index using natural organic pigments which fluoresce when exposed to UV radiation. In combination with an optical fiber, we have built a prototype sensor based on the pigment of turmeric or "Curcuma Longa". Curcuma longa fluoresces in the range of 500 to 680 nm when exposed to UV radiation. The system uses a filter to isolate the sunlight UV component. The sensor measures the variation in fluorescence intensity using a light dependent resistor to determine radiation levels and correlate it with the UV index. The sensor has been tested in Loja, Ecuador which is located at the equator (UV levels can reach up to 20.0 at the equator). When compared to a standard commercially available sensor (ML8511/LAPIS Semiconductor) this prototype has an error of ± 2.8%. We will describe the optical design and present measurements made with this novel inexpensive sensor.

Halide perovskites are very attractive for solution-processed visible and near-IR sensing applications due to their intrinsic advantages such as excellent photosensitivity, bandgap tunability, broadband sensitivity, high charge transport capability, and solution-processability. Unlike Pb-based perovskites, which cannot be tuned to below 1.48 eV, Pb-Sn mixed halide perovskites exhibit low bandgaps of 1.2-1.3 eV. Due to the low bandgap, these Pb-Sn mixed halide perovskite can absorb light till 1000nm making them a viable alternative to Silicon as the visible and near-IR broadband photodetectors. However, the low-bandgap nature of Pb-Sn mixed perovskites also causes large levels of electron and hole injection from anode and cathode, thus leading to high dark current. To mitigate the issue of charge injection, therefore, it is important to have an electron blocking layer (EBL) and a hole blocking layer (HBL) inserted between the electrodes and the Pb-Sn mixed perovskite photodetectors.

In the area of environmental monitoring, Volatile Organic Compounds (VOCs) have become a major concern. Specifically, in indoor environments, VOCs have been found to be linked with various health conditions-ranging from benign to lethal. Early detection of VOC gases can play a crucial role in ensuring a safe environment. In this work, we have looked into two different geometrical arrangements of methylammonium lead iodide (MAPbI₃) perovskite to study how their selectivity and sensitivity towards an array of VOC gases under different illumination conditions may be affected. For the purpose of a comparative study, we tested the sensitivity of the device using two different photo-resistor designs, namely, (a) capillary-filled microchannels, where microchannels were created on indium tin oxide (ITO) coated plastic substrate, and leveraging the capillary motion force the microchannels were filled with the perovskite precursor solution, and (b) thin-film approach, where perovskite layers were spin coated on substrates with two conductive pads across. Samples of both designs were exposed to four analytes: acetone, ethanol, isopropanol, and methanol. In our previous study on the capillary design, we reported a decrease in photocurrent by about 22% upon exposure to methanol under illuminated conditions. The goal of this comparative study is to identify the viability of the photo-resistor design for fabricating a low-cost and fast-response gas sensor for the purpose of environmental monitoring.

Here, we report on an all-organic solid-state radiation dosimeter patterned onto a plastic substrate that allows for real-time measurements communicated over WiFi. The “sense” area and the conductive traces are made using low-conductivity PEDOT:PSS, and measurements are read out by a low-current op-amp. As the detector is subjected to radiation, the ionized air, substrate, and sense area cause a charge accumulation which is then read out as a voltage from the op-amp. OFETs on either side of the sense area allow for the charge to be cleared, allowing for accurate dose measurement without saturation. Additionally, the inclusion of a PEDOT:PSS ground plane as the first layer on the PEN substrate helps to shield the sensor itself from extraneous static. For X-rays, the limit of detection is approximately 5 mRad/min, and for gamma rays the limit is approximately 5 mRad/hr. Through appropriate control of the clearing OFETs, the device is quickly reset to allow for a continuous measurement.

Controlling the amount of radiation that a cancer patient receives during treatment is critical to ensure the intended treatment outcome. In this work we use small molecule organic semiconductor devices as radiation sensors/dosimeters which have an effective Z close to that of human tissue. Solution processing provides excellent opportunities for scalability on flexible substrates, allowing them to conform to skin and clothing, and enabling dose measurement at the point of entry to the human body. Previous work using organic field-effect transistors (OFETs) for radiation detection has focused on radiation doses much greater than received by patients during cancer diagnostic imaging and treatment, while this work focuses on the response of OFET-based sensors at low doses relevant to cancer treatment. A systematic change in the threshold voltage of the FETs was observed with cumulative dose. Our results demonstrate that OFETs may be used in dosimetry applications for oncology.

OLEDs have many attractive features as light sources for applications in biology and medicine. Photodynamic therapy (PDT) involves the use of light, a photosensitizer and oxygen to kill target cells which can be cancer, bacteria, parasites or fungi. There is a growing realisation that PDT may not only be useful for treating cancers, but also for the growing problem of antimicrobial resistance. This talk will describe the development of OLEDs for PDT, taking account of the particular needs of this application in terms of size, wavelength, light output, uniformity and lifetime. It will show work towards achieving high uniformity at high light output (~10 mW/cm2) over a substantial area and examples of antimicrobial applications.

Hybrid perovskite materials are attractive for detection of X-ray and gamma-ray in both direct and indirect ways. The high stopping power of perovskites as well as excellent charge transport properties enables direct detection of single photon gamma ray in photon counting mode. The strong absorption of UV-vis light by most hybrid perovskites also enable very sensitive photodetectors which can count the emitted photons from scintillators under radiation. In addition, many perovskite compositions are also explored for scintillator applications. I am going to review the progress made at UNC on these three main research directions.

There is a growing need for curved X-ray detectors for use in medical, industrial, and security applications for imaging of complex shapes. Fabrication of such curved X-ray detectors require materials that can sustain mechanical stresses. Organic-inorganic hybrid X-ray detectors consisting of high atomic number nanoparticles in an organic bulk heterojunction matrix has the potential to enable this. However organic semiconductors can crystallise depending on their molecular weight, thereby restricting deformation. In this study, we evaluate the influence of the molecular weight of organic semiconductors on the inherent strain in such hybrid detectors. We demonstrate that a careful selection of molecular weight and substrate thickness is a necessity to enable curved detectors. Based on optimised combinations, we show that such detectors can be curved to a very small radius of curvatures approaching 1 mm which ensures compatibility for applications in a multitude of fields.

In this presentation, we report an ultraflexible magnetic sensor matrix system comprising a 2 × 4 array of magnetoresistance sensors, a bootstrap organic shift register driving the matrix, and organic voltage amplifiers integrated within a 3-µm-thick polymer substrate. The system demonstrates high magnetic sensitivity owing to the use of organic amplifiers. Moreover, the shift register enabled real-time mapping of 2D magnetic field distribution. These ultraflexible magnetic sensor systems integrated with organic multifunctional circuits are suitable for use in position control systems used in applications such as soft robots, wearable electronics, and smart textiles.

Antibiotic residues are regulated in commercially produced milk, with elevated concentrations being harmful. Detection of these antibiotic residues in milk pose a significant challenge for supply chain stakeholders due to the industry standard practice of low-interval off-site laboratory testing. This practice poses risk of non-compliant milk going undetected during on-site milk collection. On-site microfluidic technologies with integrated optical sensors are positioned to mitigate this challenge using increased screening intervals. Droplet-based (digital) microfluidic systems show promise to provide highthroughput screening in dairy applications with integrated fluorescence spectroscopy technologies. However, conventional digital microfluidic systems are subject to biofouling from the protein and fat content within milk. In this work, a biofouling-resistant digital microfluidic platform is introduced. The digital microfluidic platform leverages advancements in parafilm layers, and is demonstrated with actuation of milk and water microdroplets. Electrowetting-based microdroplet actuation is achieved via scalable grid arrays of uniplanar printed surface electrodes in open and closed system configurations. For this array technology, a reconfigurable firmware is developed for user control of automated microdroplet actuation at up to three hundred volts using a graphical computer interface. An exposition of the microdroplet actuation performance is demonstrated and assessed through an optical system for closed-open feedback and positioning of microdroplets. This optical closed-loop allows the actuation velocity of microdroplets to be characterized for polydimethylsiloxane and parafilm dielectric layers, for both water and milk as a function of frequency and voltage. Scalability and automation of the microfluidic platform is discussed, and future integration of fluorescence spectroscopy is investigated.

In recent years, optoelectronic devices are implemented based on natural DNA with enhanced performance and efficiency. In this study, we present stimulus pulse-dependent responses in natural DNA biopolymer devices. The device consists of a simple sandwich structure and the resistivity can be manipulated with respect to voltage operation. We characterize the stimulus pulse-dependent responses, where the synaptic plasticity will be presented. To further explore dynamics of resistive states, the effect of incorporating a photo-responsive material on the light-triggered electrical characteristics will be discussed. Our results reveal natural DNA biopolymer shows great promise for the development of synaptic devices for neuromorphic circuitry.

Most electrical sensor and biosensors elements require reliable transducing elements to convert small potential changes into easy to read out current signals. Offering inherent signal magnification and being operable in many relevant environments field-effect transistors (FETs) are the element of choice in may cases. In particular using electrolyte gating numerus sensors and biosensors have been realized in aqueous environments. Over the past yeas electrolyte gated FETs have been fabricated using a variety of semiconducting materials including graphene, ZnO as well as conjugated molecules and polymers. In particular using conducting polymers top performing devices have been achieved. Here we present an approach to use a transition metal dichalcogenide (TMDCs) based monolayer device. Using MoS2 monolayers we show that such electrolyte gated devices may be regarded as very promising future transducing elements for sensor and biosensor applications.

The seamless integration of electronics with biology requires new bio-inspired approaches that, analogously to nature, rely on the presence of electrolytes for signal multiplexing. On the contrary, conventional multiplexing schemes mostly rely on electronic carriers and require peripheral circuitry for their implementation, which imposes limitations toward their adoption in bio-applications. Here we show an iontronic multiplexer based on spatiotemporal dynamics of organic electrochemical transistors (OECTs), with an electrolyte as the shared medium of communication. The iontronic system discriminates locally random-access events with no need of peripheral circuitry, thus deceasing significantly the integration complexity. The form factors of OETCs, open new avenues for unconventional multiplexing in the emerging fields of bioelectronics and neuromorphic sensors. Examples of organic neuromorphic electronics for local learning in applications with energy restrictions are also showcased.

Polymer, organic, and graphene based chemical sensors have shown excellent performance as chemical sensors. They can be chemically modified with receptor groups to provide additional sensitivity and selectivity. We propose and will demonstrate a three-synapse neuromorphic circuit for chemical sensing and olfactory pattern recognition. The circuit is implemented with 180 nm silicon technology and the sensing synapses can be incorporated in a back-end-of-the-line process on the silicon chip or be fabricated separately and electrically connected to the rest of the circuit. Our neuromorphic circuit is designed to be suited for analyzing mixtures of two analytes. We will present both simulation results and experimental data. The active sensing material for the sensing synapses can include conducting polymers such as PEDOT, monolayer graphene, reduced graphene oxide, copper phthalocyanine, as well as other materials.

Narrow bandgap lead sulfide (PbS) quantum dots (QDs) are solution-processed materials used for optoelectronic applications in the short-wavelength infrared (SWIR) range (1400 - 3000 nm). The PbS QDs based photodetector has achieved comparable detectivity with current commercial SWIR sensors. However, there are still obstacles towards commercialization in commonly used layer by layer (LbL) deposition, such as high material consumption and low reproducibility. Here, we developed a new ligand exchange strategy to prepare ligand exchanged QD inks for single-step PbS film deposition. Compared with LbL deposition, the EQE of PbS QD photodetector made by single-step deposition has improved from 31% to 53%. The EQE and responsivity can be further improved to 95% with IR transparent electrode.