Phase-separated porous nanocomposite with ultralow percolation threshold for wireless bioelectronics.

Realizing the full potential of stretchable bioelectronics in wearables, biomedical implants and soft robotics necessitates conductive elastic composites that are intrinsically soft, highly conductive and strain resilient. However, existing composites usually compromise electrical durability and performance due to disrupted conductive paths under strain and rely heavily on a high content of conductive filler. Here we present an in situ phase-separation method that facilitates microscale silver nanowire assembly and creates self-organized percolation networks on pore surfaces. The resultant nanocomposites are highly conductive, strain insensitive and fatigue tolerant, while minimizing filler usage. Their resilience is rooted in multiscale porous polymer matrices that dissipate stress and rigid conductive fillers adapting to strain-induced geometry changes. Notably, the presence of porous microstructures reduces the percolation threshold (Vc = 0.00062) by 48-fold and suppresses electrical degradation even under strains exceeding 600%. Theoretical calculations yield results that are quantitatively consistent with experimental findings. By pairing these nanocomposites with near-field communication technologies, we have demonstrated stretchable wireless power and data transmission solutions that are ideal for both skin-interfaced and implanted bioelectronics. The systems enable battery-free wireless powering and sensing of a range of sweat biomarkers-with less than 10% performance variation even at 50% strain. Ultimately, our strategy offers expansive material options for diverse applications.

Imaging neuro-urodynamics of mouse major pelvic ganglion with a micro-endoscopic approach.

Postganglionic neurons of the autonomic nervous system lie outside of the central nervous system and innervate specific target effectors such as organs or glands. The major pelvic ganglion (MPG) is one such ganglion that plays a significant role in controlling bladder function in rodents. However, because of technical and physical constraints in recording electrophysiological signals from these neurons in vivo, the functional neural activity in MPG is mostly unknown. Transgenic animal models expressing genetically encoded calcium indicators now provide opportunities to monitor the activity of populations of neurons in vivo to overcome these challenges related to traditional electrophysiological methods. However, like many peripheral neurons, the MPG is not conducive to conventional fluorescent microscopy techniques, as it is located in the pelvic cavity, thus limiting robust optical access by benchtop microscopes. Here, we present an endoscopic approach based on a custom miniscope system (UCLA V3) that allows for effective in vivo monitoring of neural activity in the MPG for the first time. We show that our imaging approach can monitor activity of hundreds of MPG neurons simultaneously during the filling and emptying of the bladder in a urethane-anesthetized transgenic mouse line expressing GCaMP6s in cholinergic MPG neurons. By using custom analysis scripts, we isolated the activity of hundreds of individual neurons and show that populations of neurons have distinct phasic activation patterns during sequential bladder filling and voiding events. Our imaging approach can be adapted to record activity from autonomic neurons across different organs and systems in both healthy and disease models.NEW & NOTEWORTHY The functional activity and information processing within autonomic ganglia is mostly unknown because of technical and physical constraints in recording electrophysiological signals from these neurons in vivo. Here, we use a micro-endoscopic approach to measure in vivo functional activity patterns from a population of autonomic neurons controlling bladder function for the first time. This approach can be adapted to record activity from autonomic neurons across different organs and systems in both healthy and disease models.

A neural network model for timing control with reinforcement.

How do humans and animals perform trial-and-error learning when the space of possibilities is infinite? In a previous study, we used an interval timing production task and discovered an updating strategy in which the agent adjusted the behavioral and neuronal noise for exploration. In the experiment, human subjects proactively generated a series of timed motor outputs. Positive or negative feedback was provided after each response based on the timing accuracy. We found that the sequential motor timing varied at two temporal scales: long-term correlation around the target interval due to memory drifts and short-term adjustments of timing variability according to feedback. We have previously described these two key features of timing variability with an augmented Gaussian process, termed reward-sensitive Gaussian process (RSGP). In a nutshell, the temporal covariance of the timing variable was updated based on the feedback history to recreate the two behavioral characteristics mentioned above. However, the RSGP was mainly descriptive and lacked a neurobiological basis of how the reward feedback can be used by a neural circuit to adjust motor variability. Here we provide a mechanistic model and simulate the process by borrowing the architecture of recurrent neural networks (RNNs). While recurrent connection provided the long-term serial correlation in motor timing, to facilitate reward-driven short-term variations, we introduced reward-dependent variability in the network connectivity, inspired by the stochastic nature of synaptic transmission in the brain. Our model was able to recursively generate an output sequence incorporating internal variability and external reinforcement in a Bayesian framework. We show that the model can generate the temporal structure of the motor variability as a basis for exploration and exploitation trade-off. Unlike other neural network models that search for unique network connectivity for the best match between the model prediction and observation, this model can estimate the uncertainty associated with each outcome and thus did a better job in teasing apart adjustable task-relevant variability from unexplained variability. The proposed artificial neural network model parallels the mechanisms of information processing in neural systems and can extend the framework of brain-inspired reinforcement learning (RL) in continuous state control.

Imaging Mitochondrial Ca2+ Uptake in Astrocytes and Neurons using Genetically Encoded Ca2+ Indicators (GECIs).

Mitochondrial Ca2+ plays a critical role in controlling cytosolic Ca2+ buffering, energy metabolism, and cellular signal transduction. Overloading of mitochondrial Ca2+ contributes to various pathological conditions, including neurodegeneration and apoptotic cell death in neurological diseases. Here we present a cell-type specific and mitochondria targeting molecular approach for mitochondrial Ca2+ imaging in astrocytes and neurons in vitro and in vivo. We constructed DNA plasmids encoding mitochondria-targeting genetically encoded Ca2+ indicators (GECIs) GCaMP5G or GCaMP6s (GCaMP5G/6s) with astrocyte- and neuron-specific promoters gfaABC1D and CaMKII and mitochondria-targeting sequence (mito-). For in vitro mitochondrial Ca2+ imaging, the plasmids were transfected in cultured astrocytes and neurons to express GCaMP5G/6s. For in vivo mitochondrial Ca2+ imaging, adeno-associated viral vectors (AAVs) were prepared and injected into the mouse brains to express GCaMP5G/6s in mitochondria in astrocytes and neurons. Our approach provides a useful means to image mitochondrial Ca2+ dynamics in astrocytes and neurons to study the relationship between cytosolic and mitochondrial Ca2+ signaling, as well as astrocyte-neuron interactions.

Widespread functional opsin transduction in the rat cortex via convection-enhanced delivery optimized for horizontal spread.

BACKGROUND: Widespread opsin expression in the cortex of rats, where transgenic models have not been established, is not practical to achieve with the traditional diffusion-based virus transduction methods (DBD). NEW METHOD: We developed protocols for convection-enhanced delivery (CED) of virus for optogenetic transduction of the rat cortex. Targeting the motor forelimb area as an example, we performed dual-site CED (6µL of virus per site, 3mm pitch between sites) in the rat motor cortex. RESULTS: We identified injection parameters optimized for horizontal spread of infusate in the agarose gel model and then demonstrated in vivo widespread opsin expression over the cortical area (7.4±1.0mm in the AP direction, 4.4±1.1mm in the ML direction, N=13 rats) using CED. The optogenetic transduction was also functionally robust, in which both optical modulation of neuronal activity and elicitation of overt motor responses was reliably observed. COMPARISON WITH EXISTING METHOD(S): CED led to about 24-fold increase in the volume of opsin expression, compared with the conventional DBD method. The total injection time was also reduced by at least 10 times, if similar extent of expression were to be achieved with the conventional DBD method. CONCLUSIONS: CED is a reliable and effective method of virus delivery for optogenetic transduction of planar superficial structures, such as the cortex in rats.

Cerebellar granule cells acquire a widespread predictive feedback signal during motor learning.

Cerebellar granule cells, which constitute half the brain's neurons, supply Purkinje cells with contextual information necessary for motor learning, but how they encode this information is unknown. Here we show, using two-photon microscopy to track neural activity over multiple days of cerebellum-dependent eyeblink conditioning in mice, that granule cell populations acquire a dense representation of the anticipatory eyelid movement. Initially, granule cells responded to neutral visual and somatosensory stimuli as well as periorbital airpuffs used for training. As learning progressed, two-thirds of monitored granule cells acquired a conditional response whose timing matched or preceded the learned eyelid movements. Granule cell activity covaried trial by trial to form a redundant code. Many granule cells were also active during movements of nearby body structures. Thus, a predictive signal about the upcoming movement is widely available at the input stage of the cerebellar cortex, as required by forward models of cerebellar control.

Transparent intracortical microprobe array for simultaneous spatiotemporal optical stimulation and multichannel electrical recording.

Optogenetics, the selective excitation or inhibition of neural circuits by light, has become a transformative approach for dissecting functional brain microcircuits, particularly in in vivo rodent models, owing to the expanding libraries of opsins and promoters. Yet there is a lack of versatile devices that can deliver spatiotemporally patterned light while performing simultaneous sensing to map the dynamics of perturbed neural populations at the network level. We have created optoelectronic actuator and sensor microarrays that can be used as monolithic intracortical implants, fabricated from an optically transparent, electrically highly conducting semiconductor ZnO crystal. The devices can perform simultaneous light delivery and electrical readout in precise spatial registry across the microprobe array. We applied the device technology in transgenic mice to study light-perturbed cortical microcircuit dynamics and their effects on behavior. The functionality of this device can be further expanded to optical imaging and patterned electrical microstimulation.

Modulating dopamine release by optogenetics in transgenic mice reveals terminal dopaminergic dynamics.

Dopamine (DA) release and uptake dynamics in the nucleus accumbens (NAc) have important implications for neurological diseases and mammalian animal behaviors. We demonstrate here the use of cell-type-specific optogenetic targeting in conjunction with fast-scan cyclic voltammetry applied to brain slices prepared from specifically tailored transgenic mice, which conditionally express channelrhodopsin-2 (ChR2) through dopamine transporter (DAT)-Cre. Terminal dopaminergic dynamics and the direct manipulation of induced DA release level by controlling light intensity, pulse width, and the shape of stimulation waveforms were studied. Effective cell terminal-targeting optogenetic induction of DA release at physiological levels in NAc is demonstrated and discussed. It was found that delivering more light energy by increasing stimulation intensity and length is not the only way to control DA release; the temporal shape of the stimulus waveform at light onset is also critically related to induced DA concentrations. In addition, DA uptake dynamics as well as the recovery of the presynaptic releasable DA pool are studied and modeled. More broadly, our experimental findings provide important further evidence for effectively applying optogenetics to induce neurotransmitter release in the behaviorally relevant region of the brain in a highly cell-type selective context.

Modified toolbox for optogenetics in the nonhuman primate.

Attracted by the appealing advantages of optogenetics, many nonhuman primate labs are attempting to incorporate this technique in their experiments. Despite some reported successes by a few groups, many still find it difficult to develop a reliable way to transduce cells in the monkey brain and subsequently monitor light-induced neuronal activity. Here, we describe a methodology that we have developed and successfully deployed on a regular basis with multiple monkeys. All devices and accessories are easy to obtain and results using these have been proven to be highly replicable. We developed the "in-chair" viral injection system and used tapered and thinner fibers for optical stimulation, which significantly improved the efficacy and reduced tissue damage. With these methods, we have successfully transduced cells in multiple monkeys in both deep and shallow cortical areas. We could reliably obtain neural modulation for months after injection, and no light-induced artifacts were observed during recordings. Further experiments using these methods have shown that optogenetic stimulation can be used to bias spatial attention in a visual choice discrimination task in a way comparable to electrical microstimulation, which demonstrates the potential use of our methods in both fundamental research and clinical applications.

Optogenetically induced spatiotemporal gamma oscillations and neuronal spiking activity in primate motor cortex.

Transient gamma-band (40-80 Hz) spatiotemporal patterns are hypothesized to play important roles in cortical function. Here we report the direct observation of gamma oscillations as spatiotemporal waves induced by targeted optogenetic stimulation, recorded by intracortical multichannel extracellular techniques in macaque monkeys during their awake resting states. Microelectrode arrays integrating an optical fiber at their center were chronically implanted in primary motor (M1) and ventral premotor (PMv) cortices of two subjects. Targeted brain tissue was transduced with the red-shifted opsin C1V1(T/T). Constant (1-s square pulses) and ramp stimulation induced narrowband gamma oscillations during awake resting states. Recordings across 95 microelectrodes (4 × 4-mm array) enabled us to track the transient gamma spatiotemporal patterns manifested, e.g., as concentric expanding and spiral waves. Gamma oscillations were induced well beyond the light stimulation volume, via network interactions at distal electrode sites, depending on optical power. Despite stimulation-related modulation in spiking rates, neuronal spiking remained highly asynchronous during induced gamma oscillations. In one subject we examined stimulation effects during preparation and execution of a motor task and observed that movement execution largely attenuated optically induced gamma oscillations. Our findings demonstrate that, beyond previously reported induced gamma activity under periodic drive, a prolonged constant stimulus above a certain threshold may carry primate motor cortex network dynamics into gamma oscillations, likely via a Hopf bifurcation. More broadly, the experimental capability in combining microelectrode array recordings and optogenetic stimulation provides an important approach for probing spatiotemporal dynamics in primate cortical networks during various physiological and behavioral conditions.

Detection of optogenetic stimulation in somatosensory cortex by non-human primates--towards artificial tactile sensation.

Neuroprosthesis research aims to enable communication between the brain and external assistive devices while restoring lost functionality such as occurs from stroke, spinal cord injury or neurodegenerative diseases. In future closed-loop sensorimotor prostheses, one approach is to use neuromodulation as direct stimulus to the brain to compensate for a lost sensory function and help the brain to integrate relevant information for commanding external devices via, e.g. movement intention. Current neuromodulation techniques rely mainly of electrical stimulation. Here we focus specifically on the question of eliciting a biomimetically relevant sense of touch by direct stimulus of the somatosensory cortex by introducing optogenetic techniques as an alternative to electrical stimulation. We demonstrate that light activated opsins can be introduced to target neurons in the somatosensory cortex of non-human primates and be optically activated to create a reliably detected sensation which the animal learns to interpret as a tactile sensation localized within the hand. The accomplishment highlighted here shows how optical stimulation of a relatively small group of mostly excitatory somatosensory neurons in the nonhuman primate brain is sufficient for eliciting a useful sensation from data acquired by simultaneous electrophysiology and from behavioral metrics. In this first report to date on optically neuromodulated behavior in the somatosensory cortex of nonhuman primates we do not yet dissect the details of the sensation the animals exerience or contrast it to those evoked by electrical stimulation, issues of considerable future interest.

A coaxial optrode as multifunction write-read probe for optogenetic studies in non-human primates.

BACKGROUND: Advances in optogenetics have led to first reports of expression of light-gated ion-channels in non-human primates (NHPs). However, a major obstacle preventing effective application of optogenetics in NHPs and translation to optogenetic therapeutics is the absence of compatible multifunction optoelectronic probes for (1) precision light delivery, (2) low-interference electrophysiology, (3) protein fluorescence detection, and (4) repeated insertion with minimal brain trauma. NEW METHOD: Here we describe a novel brain probe device, a "coaxial optrode", designed to minimize brain tissue damage while microfabricated to perform simultaneous electrophysiology, light delivery and fluorescence measurements in the NHP brain. The device consists of a tapered, gold-coated optical fiber inserted in a polyamide tube. A portion of the gold coating is exposed at the fiber tip to allow electrophysiological recordings in addition to light delivery/collection at the tip. RESULTS: Coaxial optrode performance was demonstrated by experiments in rodents and NHPs, and characterized by computational models. The device mapped opsin expression in the brain and achieved precisely targeted optical stimulation and electrophysiology with minimal cortical damage. COMPARISON WITH EXISTING METHODS: Overall, combined electrical, optical and mechanical features of the coaxial optrode allowed a performance for NHP studies which was not possible with previously existing devices. CONCLUSIONS: Coaxial optrode is currently being used in two NHP laboratories as a major tool to study brain function by inducing light modulated neural activity and behavior. By virtue of its design, the coaxial optrode can be extended for use as a chronic implant and multisite neural stimulation/recording.

Widespread state-dependent shifts in cerebellar activity in locomoting mice.

Excitatory drive enters the cerebellum via mossy fibers, which activate granule cells, and climbing fibers, which activate Purkinje cell dendrites. Until now, the coordinated regulation of these pathways has gone unmonitored in spatially resolved neuronal ensembles, especially in awake animals. We imaged cerebellar activity using functional two-photon microscopy and extracellular recording in awake mice locomoting on an air-cushioned spherical treadmill. We recorded from putative granule cells, molecular layer interneurons, and Purkinje cell dendrites in zone A of lobule IV/V, representing sensation and movement from trunk and limbs. Locomotion was associated with widespread increased activity in granule cells and interneurons, consistent with an increase in mossy fiber drive. At the same time, dendrites of different Purkinje cells showed increased co-activation, reflecting increased synchrony of climbing fiber activity. In resting animals, aversive stimuli triggered increased activity in granule cells and interneurons, as well as increased Purkinje cell co-activation that was strongest for neighboring dendrites and decreased smoothly as a function of mediolateral distance. In contrast with anesthetized recordings, no 1-10 Hz oscillations in climbing fiber activity were evident. Once locomotion began, responses to external stimuli in all three cell types were strongly suppressed. Thus climbing and mossy fiber representations can shift together within a fraction of a second, reflecting in turn either movement-associated activity or external stimuli.

An amplified promoter system for targeted expression of calcium indicator proteins in the cerebellar cortex.

Recording of identified neuronal network activity using genetically encoded calcium indicators (GECIs) requires labeling that is cell type-specific and bright enough for the detection of functional signals. However, specificity and strong expression are often not achievable using the same promoter. Here we present a combinatorial approach for targeted expression and single-cell-level quantification in which a weak promoter is used to drive trans-amplification under a strong general promoter. We demonstrated this approach using recombinant adeno-associated viruses (rAAVs) to deliver the sequence of the GECI D3cpv in the mouse cerebellar cortex. Direct expression under the human synapsin promoter (hSYN) led to high levels of expression (50-100 µM) in five interneuron types of the cerebellar cortex but not in Purkinje cells (PCs) (≤10 µM), yielding sufficient contrast to allow functional signals to be recorded from somata and processes in awake animals using two-photon microscopy. When the hSYN promoter was used to drive expression of the tetracycline transactivator (tTA), a second rAAV containing the bidirectional TET promoter (P(tet)bi) could drive strong D3cpv expression in PCs (10-300 µM), enough to allow reliable complex spike detection in the dendritic arbor. An amplified approach should be of use in monitoring neural processing in selected cell types and boosting expression of optogenetic probes. Additionally, we overcome cell toxicity associated with rAAV injection and/or local GECI overexpression by combining the virus injection with systemic pre-injection of hyperosmotic D-mannitol, and by this double the time window for functional imaging.

Integrated device for combined optical neuromodulation and electrical recording for chronic in vivo applications.

Studying brain function and its local circuit dynamics requires neural interfaces that can record and stimulate the brain with high spatiotemporal resolution. Optogenetics, a technique that genetically targets specific neurons to express light-sensitive channel proteins, provides the capability to control central nervous system neuronal activity in mammals with millisecond time precision. This technique enables precise optical stimulation of neurons and simultaneous monitoring of neural response by electrophysiological means, both in the vicinity of and distant to the stimulation site. We previously demonstrated, in vitro, the dual capability (optical delivery and electrical recording) while testing a novel hybrid device (optrode-MEA), which incorporates a tapered coaxial optical electrode (optrode) and a 100 element microelectrode array (MEA). Here we report a fully chronic implant of a new version of this device in ChR2-expressing rats, and demonstrate its use in freely moving animals over periods up to 8 months. In its present configuration, we show the device delivering optical excitation to a single cortical site while mapping the neural response from the surrounding 30 channels of the 6 × 6 element MEA, thereby enabling recording of optically modulated single-unit and local field potential activity across several millimeters of the neocortical landscape.

Approaches to optical neuromodulation from rodents to non-human primates by integrated optoelectronic devices.

Methods on rendering neurons in the central nervous system to be light responsive has led to a boom in using optical neuromodulation as a new approach for controlling brain states and understanding neural circuits. In addition to the developing versatility to "optogenetically" labeling of neural cells and their subtypes by microbiological methods, parallel efforts are under way to design and implement optoelectronic devices to achieve simultaneous optical neuromodulation and electrophysiological recording with high spatial and temporal resolution. Such new device-based technologies need to be developed for full exploitation of the promise of optogenetics. In this paper we present single- and multi-element optoelectronic devices developed in our laboratories. The single-unit element, namely the coaxial optrode, was utilized to characterize the neural responses in optogenetically modified rodent and primate models. Furthermore, the multi-element device, integrating the optrode with a 6×6 microelectrode array, was used to characterize the spatiotemporal spread of neural activity in response to single-site optical stimulation in freely moving rats. We suggest that the particular approaches we employed can lead to the emergence of methods where spatio-temporal optical modulation is integrated with real-time read out from neural populations.

Reliable coding emerges from coactivation of climbing fibers in microbands of cerebellar Purkinje neurons.

The inferior olive projects climbing fiber axons to cerebellar Purkinje neurons, where they trigger calcium-based dendritic spikes. These responses dynamically shape the immediate spike output of Purkinje cells as well as provide an instructive signal to guide long-term plasticity. Climbing fibers typically fire approximately once a second, and the instructive role is distributed over many such firing events. However, transmission of salient information on an immediate basis needs to occur on a shorter timescale during which a Purkinje cell would typically be activated by a climbing fiber only once. Here we show using in vivo calcium imaging in anesthetized mice and rats that sensory events are rapidly and reliably represented by momentary, simultaneous coactivation of microbands of adjacent Purkinje cells. Microbands were sagittally oriented and spanned up to 100 microm mediolaterally, representing hundreds of Purkinje cells distributed over multiple folia. Spontaneous and sensory-evoked microbands followed boundaries that were close or identical to one another and were desynchronized by olivary injection of the gap junction blocker mefloquine, indicating that excitation to the olive is converted to synchronized firing by electrical coupling. One-time activation of microbands could distinguish a sensory response from spontaneous activity with up to 98% accuracy. Given the anatomy of the olivocerebellar system, microband synchrony may shape the output of neurons in the cerebellar nuclei either via powerful inhibition by Purkinje cells or by direct monosynaptic excitation from the inferior olive.

Identification and clustering of event patterns from in vivo multiphoton optical recordings of neuronal ensembles.

In vivo multiphoton fluorescence microscopy allows imaging of cellular structures in brain tissue to depths of hundreds of micrometers and, when combined with the use of activity-dependent indicator dyes, opens the possibility of observing intact, functioning neural circuitry. We have developed tools for analyzing in vivo multiphoton data sets to identify responding structures and events in single cells as well as patterns of activity within the neural ensemble. Data were analyzed from populations of cerebellar Purkinje cell dendrites, which generate calcium-based complex action potentials. For image segmentation, active dendrites were identified using a correlation-based method to group covarying pixels. Firing events were extracted from dendritic fluorescence signals with a 95% detection rate and an 8% false-positive rate. Because an event that begins in one movie frame is sometimes not detected until the next frame, detection delays were compensated using a likelihood-based correction procedure. To identify groups of dendrites that tended to fire synchronously, a k-means-based procedure was developed to analyze pairwise correlations across the population. Because repeated runs of k-means often generated dissimilar clusterings, the runs were combined to determine a consensus cluster number and composition. This procedure, termed meta-k-means, gave clusterings as good as individual runs of k-means, was independent of random initial seeding, and allowed the exclusion of outliers. Our methods should be generally useful for analyzing multicellular activity recordings in a variety of brain structures.

A microelectrode/microelectronic hybrid device for brain implantable neuroprosthesis applications.

We have designed, fabricated, and characterized a microminiaturized "neuroport" for brain implantable neuroprosthesis applications, using an analog CMOS integrated circuit and a silicon based microelectrode array. An ultra-low power, low-noise CMOS preamplifier array with integral multiplexing was designed to accommodate stringent thermal and electrophysiological requirements for implantation in the brain, and a hybrid integration approach was developed to fabricate a functional microminiaturized neuroprobe device. Measurements showed that our fully scalable 16-channel CMOS amplifier chip had an average gain of 44 dB, bandwidth from 10 Hz to 7.3 kHz, and an equivalent input noise of approximately 9 microVrms with an average power consumption per preamplifier of 52 microW, which is consistent with simulation results. As a proof-of-concept demonstration, we have measured local field potentials from thalamocortical brain slices of rats, showing oscillatory behavior with an amplitude about 0.5 mV and a period ranging 80-120 ms. The results suggest that the hybrid integrated neuroport can form a prime platform for the development of a next level microminiaturized neural interface to the brain in a single implantable unit.

Application of light-emitting diodes for aerosol fluorescence detection.

We demonstrate a proof-of-concept optical spectroscopic system for bioaerosol-particle fluorescence detection, in which a pulsed high-power laser is replaced by a highly compact linear array of sequentially fired light from blue light-emitting diodes. The results suggest that low-cost, compact optical aerosol detection may be feasible with the contemporary emergence of efficient UV light-emitting diodes.