Biology subjects

Chitnis, P. V.

Publications and source records attributed to Chitnis, P. V..

5 recordsLinked to original sources

bioRxiv2026

Frequency modulated semi-continuous wave Doppler ultrasound: A novel method for the detection of scatterer velocity and range using wearable ultrasound instrumentation

Doppler ultrasound imaging has become a key tool for clinicians and researchers to measure the velocity of blood and tissues within the human body. Presently pulsed wave and continuous wave Doppler imaging dominate the space as the two most prominent methods and are considered distinct from one another. However, these two techniques can also be considered as ends of a continuum along which Doppler imaging and phase tracking techniques exist. At the midpoint between these methods exists another underexplored Doppler imaging technique we refer to as frequency modulated semi-continuous wave (FMSCW) Doppler. We present a full technical overview of this technique, simulations exploring the impact of selected imaging parameters as well as how noise impacts imaging, and present three exemplary imaging sessions collected from human participants using FMSCW Doppler collected from a wearable ultrasound system. The results of the simulations evaluating the impact of imaging parameters demonstrate the trade-off between resolution in the range and velocity axis as well as the impact of scatterer range and speed on the measurement error. The three sets of images collected from human participants serve to demonstrate FMSCW Doppler used in a variety of wearable ultrasound applications including cardiovascular monitoring, rehabilitation assessment, and prosthetic device control. Furthermore, we discuss the relationship between FMSCW Doppler and isomorphic techniques from radar as well as potential inspiration for improvements for FMSCW Doppler inspired by the echolocation of bats.

bioengineering↗

bioRxiv2026

Direct Synthesis of Targeted Nanosized ICG J-aggregate for Photoacoustic Imaging

Indocyanine green (ICG) J-aggregates (JAs) are self-assembled particles characterized by a sharp and strong absorption peak in the near-infrared region ([~]890 nm), enhanced photostability, low fluorescence, and high photothermal conversion efficiency, compared to monomeric ICG. These attributes make ICG-JAs promising contrast agent candidates for photoacoustic imaging (PAI). However, traditional methods for synthesizing ICG-JAs often yield particles without targeting ability, which limit their applications. Thus, to synthesize targeted nanoscale JA, complex and multi-step encapsulation and filtration processes are generally required. To solve this issue, we introduce a robust and rapid strategy for direct synthesis of targeted nanoscale ICG-JA by co-assembling ICG and ICG-azide dyes under optimized formulation conditions that do not require encapsulation. The resulting nanoscale JAAZ particles (nJAAZ) exhibit diameters of [~]120-150 nm and are amenable to direct bio-orthogonal functionalization via copper-free click chemistry for the attachment of virtually any targeting ligands and/or biomolecules. We further demonstrate the strong photoacoustic signal generation of these nJAAZ in vitro and in vivo, highlighting their potential as a modular high-performance contrast agent platform for PAI. This work establishes a scalable and tunable platform for engineering functional JAs, opening new avenues for targeted molecular imaging and theranostic applications.

bioengineering↗

bioRxiv2026

DNA-Based Nanoprobes for Fluorescence K+ Sensing in Neural Systems

SignificanceAbnormalities in potassium ion concentrations across subregions of the hippocampus have been implicated in seizures and other pathologies. Direct measurements of potassium ion concentrations are largely made using invasive electrodes, which do not allow for wide spatial coverage. This fluorescent nanoparticle potassium sensor enables direct visualization of potassium dynamics and represents a minimally invasive alternative to electrode-based methods. AimHere, we present a DNA-based fluorescence nanoprobe capable of sensing relative concentrations of potassium ions within populations of neurons. We present its effectiveness in monitoring neuronal K+ dynamics in response to electrical stimulation ex vivo. ApproachWe used widefield fluorescence microscopy to monitor changes in fluorescence intensity in labeled brain tissue in response to electrical stimulation ex vivo. ResultsWe found that our nanoprobe could be retained within the intracellular compartment and modulate in fluorescence intensity linearly in response to induced electrical current. Our K+ Sensor showed a fractional fluorescence change of approximately 1% per 10 mA of applied stimulation current in brain tissue. Optical spectroscopy confirmed the selectivity of the nanoprobes to potassium ions over other endogenous ions. ConclusionsOur findings indicate that this nanoprobe can be used to detect more complex potassium dynamics implicated in various pathologies of the nervous system, such as migraines, seizures, and trauma.

bioengineering↗

bioRxiv2025

Synthesis and Characterization of ICG-based Near-infrared Photoacoustic Contrast Agents

Near-infrared photoacoustic imaging (NIR-PAI) integrates optical excitation with ultrasound detection to enable high-resolution, deep-tissue imaging by taking advantage of reduced light scattering and absorption in this spectral window. Despite its potential, clinical translation of contrast-enhanced NIR-PAI is limited by the scarcity of effective contrast agents. Indocyanine green (ICG), an FDA-approved NIR dye, is a strong candidate due to its biocompatibility and photoacoustic efficiency. However, its concentration-dependent aggregation, lack of facile targeting strategies, instability in aqueous environments, and low photostability result in variable signal, high background noise, and reduced reliability in vivo. To address these challenges, we developed three biocompatible ICG-based nanoprobe platforms amenable to facile, scalable synthesis: 5-arm DNA-ICG nanostructures (5-arm DNA-ICG), lipid-shelled ICG nanobubbles (ICG-NBs), and Azide-modified ICG J-aggregates (JAAZ). These platforms are designed to preserve ICG monomers or control aggregation, enabling enhanced NIR-PAI performance. Spectroscopic and photoacoustic analyses revealed consistent absorbance and photoacoustic profiles, showing enhanced signals compared to free ICG. The greatest improvement was observed for JAAZ, followed by ICG-NBs and 5-arm DNA-ICG. Photostability studies showed that JAAZ aggregation protects ICG from light-induced photodegradation, whereas monomer preservation in 5-arm DNA-ICG and ICG-NBs provides less protection and moderate signal stability. All three probes demonstrated stable performance under physiological conditions, achieved strong signal-to-noise ratios at depth and under tissue-mimicking conditions, and required markedly reduced probe concentrations to generate robust signals. Their modular architectures allow incorporation of targeting ligands, offering molecular specificity and multimodal functionality. Collectively, these contrast agent platforms provide noninvasive, deep-tissue molecular imaging and biosensing, with strong potential for future preclinical and clinical translation, and represent a promising alternative to free ICG for biomedical applications.

bioengineering↗

bioRxiv2022

Size-tunable ICG-based contrast agent platform for targeted near-infrared photoacoustic imaging

Near-infrared photoacoustic imaging (NIR-PAI) combines the advantages of optical and ultrasound imaging to provide anatomical and functional information of tissues with high resolution. Although NIR-PAI is promising, its wide application is hindered by the limited availability of NIR contrast agents. J-aggregates (JA) made of indocyanine green dye (ICG) represents an attractive class of biocompatible contrast agents for PAI. Here, we present a facile synthesis method that combines ICG and ICG-azide dyes for producing contrast agent with tunable size down to 230 nm and direct functionalization with targeting moieties. The ICG-JA platform has a detectable PA signal in vitro that is two times stronger than whole blood and high photostability. The targeting ability of ICG-JA was measured in vitro using HeLa cells. The ICG-JA platform was then injected into mice and in vivo NIR-PAI showed enhanced visualization of liver and spleen for 90 minutes post-injection with a contrast-to-noise ratio of 2.42.

bioengineering↗