Ultrasensitive ultrasound imaging of gene expression with signal unmixing

Acoustic percolation switches enable targeted drug delivery controlled by diagnostic ultrasound

Delivering biomedicines to specific sites of disease using remote-controlled devices is a long-standing vision in biomedical research. However, most existing externally triggered delivery systems are based on complex micromachines that are controlled with electromagnetic waves and require custom external instrumentation. Here, we present a drug delivery platform based on a simple protein-containing hydrogel that can be both imaged and triggered to release drugs at specific locations using widely available diagnostic ultrasound devices. This technology is based on the addition of air-filled protein nanostructures called gas vesicles (GVs) to hydrogel delivery vehicles. While intact, GVs sterically block the release of drug payloads and allow the vehicle to be imaged with ultrasound. An increase in ultrasound pressure causes the collapse of GVs within the delivery vehicles at the desired anatomical location, instantly creating percolation channels in the hydrogel, massively increasing diffusivity, and leading to rapid drug release. Unlike previous ultrasound-actuated delivery approaches, both the imaging and release are performed using a simple diagnostic ultrasound probe ubiquitously available in clinical settings. We implement this concept by quantifying ultrasound-controlled drug diffusion and release in vitro and demonstrating image-guided protein delivery in vivo in the gastrointestinal (GI) tract following oral administration. We further validate this technology by using it to deliver anti-inflammatory antibodies to effectively treat a rat model of colitis. Targeted acoustic percolation switches (TAPS) open a conduit for local, image-guided drug delivery with a simple formulation and commonplace ultrasound equipment.

Excavation of acoustic nanostructures biosynthesis gene clusters by combinatorial strategy

Gas vesicles (GVs) produced by microorganisms are genetically engineered, air-filled protein nanostructures that have widespread applications in ultrasound imaging and ultrasound-mediated drug delivery. However, constrained by the shape and size, most of them are difficult to be imaged by clinical ultrasound machines, which limits their biomedical applications. Here, we constructed a hybrid gene cluster of the structural gene cluster from Serratia sp. ATCC 39006 and the accessory gene cluster from Bacillus megaterium in Escherichia coli to synthesize a novel gene-encoded gas vesicle with a width of approximately 70 nm and a length of about 100 nm, using a synthetic biology strategy, termed as ARGS1B. This new type of GVs can be stably produced in bacteria and is able to be imaged by clinical ultrasound machines in vivo and in vitro. Furthermore, the novel nanostructure can be easily engineered for different particle sizes through point saturation mutation, expanding the sources of GVs and providing new insights into the biosynthesis mechanism of GVs.

Achieving single cell acoustic localisation with deactivation super resolution

Photo-activated localization microscopy (PALM) has been a game-changer, breaking the diffraction limit in spatial resolution. This study presents the Deactivation Super Resolution (DSR) method, which utilises the deactivation of genetically encodable contrast agents, enabling us to super-resolve and pinpoint individual cells with ultrasound as they navigate through structures which cannot be resolved by conventional B-Mode imaging. DSR takes advantage of Gas Vesicles (GVs), which are air-filled sub-micron particles that have been expressed in genetically engineered bacterial and mammalian cells to produce acoustic contrast. Our experimental results show that DSR can distinguish sub-wavelength microstructures that standard B-mode ultrasound images fail to resolve by super-localising individual mammalian cells. This study provides a proof of concept for the potential of DSR to serve as a super-resolution ultrasound technique for individual cell localisation, opening new horizons in the field.

Assessing microbiota in vivo: debugging with medical imaging

The microbiota is integral to human health and has been mostly characterized through various ex vivo 'omic'-based approaches. To better understand the real-time function and impact of the microbiota, in vivo molecular imaging is required. With technologies such as positron emission tomography (PET), magnetic resonance imaging (MRI), and computed tomography (CT), insight into microbiological processes may be coupled to in vivo information. Noninvasive imaging enables longitudinal tracking of microbes and their components in real time; mapping of microbiota biodistribution, persistence and migration; and simultaneous monitoring of host physiological responses. The development of molecular imaging for clinical translation is an interdisciplinary science, with broad implications for deeper understanding of host-microbe interactions and the role(s) of the microbiome in health and disease.

A mediator-free sonogenetic switch for therapeutic protein expression in mammalian cells

An ultrasound-responsive transgene circuit can provide non-invasive, spatiotemporally precise remote control of gene expression and cellular behavior in synthetic biology applications. However, current ultrasound-based systems often rely on nanoparticles or harness ultrasound's thermal effects, posing risks of tissue damage and cellular stress that limit their therapeutic potential. Here, we present Spatiotemporal Ultrasound-induced Protein Expression Regulator (SUPER), a novel gene switch enabling mediator-free, non-invasive and direct regulation of protein expression via ultrasound in mammalian cells. SUPER leverages the mammalian reactive oxygen species (ROS) sensing system, featuring KEAP1 (Kelch-like ECH-associated protein 1), NRF2 (nuclear factor erythroid 2-related factor 2), and antioxidant response element (ARE) as its core components. We demonstrate that low-intensity (1.5 W/cm2, ∼45 kHz), brief (40 s) ultrasound exposure generates non-toxic levels of ROS, activating the KEAP1/NRF2 pathway in engineered cells and leading to the controlled expression of target gene(s) via a synthetic ARE promoter. The system exhibits robust expression dynamics, excellent reversibility, and functionality in various cell types, including human mesenchymal stem cell-derived lines (hMSC-TERT). In a proof-of-concept study, ultrasound stimulation of subcutaneously implanted microencapsulated engineered cells stably expressing the sonogenetic circuit in a type 1 diabetic mouse model triggered sufficient insulin production to restore normoglycemia. Our work highlights ultrasound's potential as a precise and non-invasive tool for advancing cell and gene therapies in personalized medicine.

Genetically engineered gas vesicle proteins with proliferative potential for synergistic targeted tumor therapy

Nanomedicine enables precision-targeted therapies through a non-invasive approach, and nanoparticles may be biologically affected during their colonization in vivo. Ensuring the efficient expression of their ex vivo performance in vivo, while ensuring biosafety, is of great significance. Previous studies have employed genetically engineered E. coli following in vivo entry as a genetically engineered targeting synergist, to enhance the effect of focused ultrasound ablation by exploiting its targeted colonization of tumor tissue. However, the proliferation process of the actual potentiating nanomaterials, i.e., the aerosol proteins produced by genetically engineered E. coli, in vivo has not been precisely observed. The authors of this paper demonstrate this spatiotemporal change in the expression of gas vesicle proteins while genetically engineered E. coli reproduces following tumor colonization. Based on their targeting and proliferative properties, the authors chose to intervene in the treatment at the maximal gas vesicle protein count to enhance the monitoring and utilization of the potentiator. By examining the therapeutic potential of the novel combination of genetic engineering and focused ultrasound, we present a robust strategy that improves the efficiency of non-invasive treatments.

Ultrasound Control of Genomic Regulatory Toolboxes for Cancer Immunotherapy

There remains a critical need for the precise control of CRISPR (clustered regularly interspaced short palindromic repeats)-based technologies. Here, we engineer a set of inducible CRISPR-based tools controllable by focused ultrasound (FUS), which can penetrate deep and induce localized hyperthermia for transgene activation. We demonstrate the capabilities of FUS-inducible CRISPR, CRISPR activation (CRISPRa), and CRISPR epigenetic editor (CRISPRee) in modulating the genome and epigenome. We show that FUS-CRISPR-mediated telomere disruption primes solid tumours for chimeric antigen receptor (CAR)-T cell therapy. We further deliver FUS-CRISPR in vivo using adeno-associated viruses (AAVs), followed by FUS-induced telomere disruption and the expression of a clinically validated antigen in a subpopulation of tumour cells, functioning as "training centers" to activate synthetic Notch (synNotch) CAR-T cells to produce CARs against a universal tumour antigen to exterminate neighboring tumour cells. The FUS-CRISPR(a/ee) toolbox hence allows the noninvasive and spatiotemporal control of genomic/epigenomic reprogramming for cancer treatment.

Harmonic imaging for nonlinear detection of acoustic biomolecules

Gas vesicles (GVs) based on acoustic reporter genes have emerged as potent contrast agents for cellular and molecular ultrasound imaging. These air-filled, genetically encoded protein nanostructures can be expressed in a variety of cell types in vivo to visualize cell location and activity or injected systemically to label and monitor tissue function. Distinguishing GV signal from tissue deep inside intact organisms requires imaging approaches such as amplitude modulation (AM) or collapse-based pulse sequences. However, these approaches have limitations either in sensitivity or require the destruction of GVs, restricting the imaging of dynamic cellular processes. To address these limitations, we developed harmonic imaging to enhance the sensitivity of nondestructive GV imaging. We hypothesized that harmonic imaging, integrated with AM, could significantly elevate GV detection sensitivity by leveraging the nonlinear acoustic response of GVs. We tested this hypothesis by imaging tissue-mimicking phantoms embedded with purified GVs, mammalian cells genetically modified to express GVs, and mice liver in vivo post-systemic infusion of GVs. Our findings reveal that harmonic cross-propagating wave AM (HxAM) imaging markedly surpasses traditional xAM in isolating GVs' nonlinear acoustic signature, demonstrating significant (p < 0.05) enhancements in imaging performance. HxAM imaging improves detection of GV producing cells up to three folds in vitro, enhances in vivo imaging performance by over 10 dB, while extending imaging depth by up to 20%. Investigation into the backscattered spectra further elucidates the advantages of harmonic imaging. These advancements bolster ultrasound's capability in molecular and cellular imaging, underscoring the potential of harmonic signals to improve GV detection.

Stretchable Ultrasound Metalens for Biomedical Zoom Imaging and Bone Quality Assessment with Subwavelength Resolution

Ultrasound imaging is extensively used in biomedical science and clinical practice. Imaging resolution and tunability of imaging plane are key performance indicators, but both remain challenging to be improved due to the longer wavelength compared with light and the lack of zoom lens for ultrasound. Here, the ultrasound zoom imaging based on a stretchable planar metalens that simultaneously achieves the subwavelength imaging resolution and dynamic control of the imaging plane is reported. The proposed zoom imaging ultrasonography enables precise bone fracture diagnosis and comprehensive osteoporosis assessment. Millimeter-scale microarchitectures of the cortical bones at different depths can be selectively imaged with a 0.6-wavelength resolution. The morphological features of bone fractures, including the shape, size and position, are accurately detected. Based on the extracted ultrasound information of cancellous bones with healthy matrix, osteopenia and osteoporosis, a multi-index osteoporosis evaluation method is developed. Furthermore, it provides additional biological information in aspects of bone elasticity and attenuation to access the comprehensive osteoporosis assessment. The soft metalens also features flexibility and biocompatibility for preferable applications on wearable devices. This work provides a strategy for the development of high-resolution ultrasound biomedical zoom imaging and comprehensive bone quality diagnosis system.

Elucidating the assembly of gas vesicles by systematic protein-protein interaction analysis

Gas vesicles (GVs) are gas-filled microbial organelles formed by unique 3-nm thick, amphipathic, force-bearing protein shells, which can withstand multiple atmospheric pressures and maintain a physically stable air bubble with megapascal surface tension. However, the molecular process of GV assembly remains elusive. To begin understanding this process, we have devised a high-throughput in vivo assay to determine the interactions of all 11 proteins in the pNL29 GV operon. Complete or partial deletions of the operon establish interdependent relationships among GV proteins during assembly. We also examine the tolerance of the GV assembly process to protein mutations and the cellular burdens caused by GV proteins. Clusters of GV protein interactions are revealed, proposing plausible protein complexes that are important for GV assembly. We anticipate our findings will set the stage for designing GVs that efficiently assemble in heterologous hosts during biomedical applications.

Characterisation of Gas Vesicles as Cavitation Nuclei for Ultrasound Therapy using Passive Acoustic Mapping

Genetically encodable gas filled particles known as gas vesicles (GVs) have shown promise as a biomolecular contrast agent for ultrasound imaging and have the potential to be used as cavitation nuclei for ultrasound therapy. In this study, we used passive acoustic mapping techniques to characterize GV-seeded cavitation, utilizing 0.5 and 1.6 MHz ultrasound over peak rarefactional pressures ranging from 100 to 2200 kPa. We found that GVs produce cavitation for the duration of the first applied pulse, up to at least 5000 cycles, but that bubble activity diminishes rapidly over subsequent pulses. At 0.5 MHz the frequency content of cavitation emissions was predominantly broadband in nature, whilst at 1.6 MHz narrowband content at harmonics of the main excitation frequency dominated. Simulations and high-speed camera imaging suggest that the received cavitation emissions come not from individual GVs but instead from the coalescence of GV-released gas into larger bubbles during the applied ultrasound pulse. These results will aid the future development of GVs as cavitation nuclei in ultrasound therapy.

Achieving Single Cell Acoustic Localisation with Deactivation Super Resolution

Super-resolution optical microscopy enables optical imaging of cells, molecules and other biological structures beyond the diffraction limit. However, no similar method exists to super-resolve specific cells with ultrasound. Here we introduce Deactivation Super Resolution (DSR), an ultrasound imaging method that uses the acoustic deactivation of genetically encodable contrast agents to super-resolve individual cells with ultrasound as they navigate through structures that cannot be resolved by conventional imaging methods. DSR takes advantage of gas vesicles, which are air-filled sub-micron protein particles that can be expressed in genetically engineered cells to produce ultrasound contrast. Our experimental results show that DSR can distinguish sub-wavelength microstructures that standard B-mode ultrasound images fail to resolve by super- localizing individual mammalian cells. This study provides a proof of concept for the potential of DSR to serve as a super- resolution ultrasound technique for individual cell localization, opening new horizons in the field.

Directed Evolution of Acoustic Reporter Genes Using High-Throughput Acoustic Screening

A major challenge in the fields of biological imaging and synthetic biology is noninvasively visualizing the functions of natural and engineered cells inside opaque samples such as living animals. One promising technology that addresses this limitation is ultrasound (US), with its penetration depth of several cm and spatial resolution on the order of 100 μm. Within the past decade, reporter genes for US have been introduced and engineered to link cellular functions to US signals via heterologous expression in commensal bacteria and mammalian cells. These acoustic reporter genes (ARGs) represent a novel class of genetically encoded US contrast agent, and are based on air-filled protein nanostructures called gas vesicles (GVs). Just as the discovery of fluorescent proteins was followed by the improvement and diversification of their optical properties through directed evolution, here we describe the evolution of GVs as acoustic reporters. To accomplish this task, we establish high-throughput, semiautomated acoustic screening of ARGs in bacterial cultures and use it to screen mutant libraries for variants with increased nonlinear US scattering. Starting with scanning site saturation libraries for two homologues of the primary GV structural protein, GvpA/B, two rounds of evolution resulted in GV variants with 5- and 14-fold stronger acoustic signals than the parent proteins. We anticipate that this and similar approaches will help high-throughput protein engineering play as large a role in the development of acoustic biomolecules as it has for their fluorescent counterparts.

SEMPER: Stoichiometric expression of mRNA polycistrons by eukaryotic ribosomes for compact, ratio-tunable multi-gene expression

Here, we present a method for expressing multiple open reading frames (ORFs) from single transcripts using the leaky scanning model of translation initiation. In this approach termed "stoichiometric expression of mRNA polycistrons by eukaryotic ribosomes" (SEMPER), adjacent ORFs are translated from a single mRNA at tunable ratios determined by their order in the sequence and the strength of their translation initiation sites. We validate this approach by expressing up to three fluorescent proteins from one plasmid in two different cell lines. We then use it to encode a stoichiometrically tuned polycistronic construct encoding gas vesicle acoustic reporter genes that enables efficient formation of the multi-protein complex while minimizing cellular toxicity. We also demonstrate that SEMPER enables polycistronic expression of recombinant monoclonal antibodies from plasmid DNA and of two fluorescent proteins from single mRNAs made through in vitro transcription. Finally, we provide a probabilistic model to elucidate the mechanisms underlying SEMPER. A record of this paper's transparent peer review process is included in the supplemental information.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

50-nm Gas-Filled Protein Nanostructures to Enable the Access of Lymphatic Cells by Ultrasound Technologies

Ultrasound imaging and ultrasound-mediated gene and drug delivery are rapidly advancing diagnostic and therapeutic methods; however, their use is often limited by the need for microbubbles, which cannot transverse many biological barriers due to their large size. Here, the authors introduce 50-nm gas-filled protein nanostructures derived from genetically engineered gas vesicles(GVs) that are referred to as 50 nmGVs. These diamond-shaped nanostructures have hydrodynamic diameters smaller than commercially available 50-nm gold nanoparticles and are, to the authors' knowledge, the smallest stable, free-floating bubbles made to date. 50 nmGVs can be produced in bacteria, purified through centrifugation, and remain stable for months. Interstitially injected 50 nmGVs can extravasate into lymphatic tissues and gain access to critical immune cell populations, and electron microscopy images of lymph node tissues reveal their subcellular location in antigen-presenting cells adjacent to lymphocytes. The authors anticipate that 50 nmGVs can substantially broaden the range of cells accessible to current ultrasound technologies and may generate applications beyond biomedicine as ultrasmall stable gas-filled nanomaterials.

Truly Tiny Acoustic Biomolecules for Ultrasound Imaging and Therapy

Nanotechnology offers significant advantages for medical imaging and therapy, including enhanced contrast and precision targeting. However, integrating these benefits into ultrasonography is challenging due to the size and stability constraints of conventional bubble-based agents. Here bicones, truly tiny acoustic contrast agents based on gas vesicles (GVs), a unique class of air-filled protein nanostructures naturally produced in buoyant microbes, are described. It is shown that these sub-80 nm particles can be effectively detected both in vitro and in vivo, infiltrate tumors via leaky vasculature, deliver potent mechanical effects through ultrasound-induced inertial cavitation, and are easily engineered for molecular targeting, prolonged circulation time, and payload conjugation.

Harmonic imaging for nonlinear detection of acoustic biomolecules

Gas vesicles (GVs) based on acoustic reporter genes have emerged as potent contrast agents for cellular and molecular ultrasound imaging. These air-filled, genetically encoded protein nanostructures can be expressed in a variety of cell types in vivo to visualize cell location and activity or injected systemically to label and monitor tissue function. Distinguishing GVs from tissue signal deep inside intact organisms requires imaging approaches such as amplitude modulation (AM) or collapse-based pulse sequences, however they have limitations in sensitivity or require irreversible collapse of the GVs that restricts its scope for imaging dynamic cellular processes. To address these limitations, this study explores the utility of harmonic imaging to enhance the sensitivity of non-destructive imaging of GVs and cellular processes. Traditional fundamental-frequency imaging utilizing cross-wave AM (xAM) sequences has been deemed optimal for GV imaging. Contrary to this, we hypothesize that harmonic imaging, integrated with xAM could significantly elevate GV detection sensitivity. To verify our hypothesis, we conducted imaging on tissue-mimicking phantoms embedded with purified GVs, mammalian cells genetically modified to express GVs, and live mice after systemic GV infusion. Our findings reveal that harmonic xAM (HxAM) imaging markedly surpasses traditional xAM in isolating GVs' nonlinear acoustic signature, showcasing significant enhancements in signal-to-background and contrast-to-background ratios across all tested samples. Further investigation into the backscattered spectra elucidates the efficacy of harmonic imaging in conjunction with xAM. HxAM imaging enables the detection of lower concentrations of GVs and cells with ultrasound and extends the imaging depth in vivo by up to 20% and imaging performance metrics by up to 10dB. These advancements bolster the capabilities of ultrasound for molecular and cellular imaging, underscoring the potential of using harmonic signals to amplify GV detection.

Photoactivated Gas-Generating Nanocontrast Agents for Long-Term Ultrasonic Imaging-Guided Combined Therapy of Tumors

To date, long-term and continuous ultrasonic imaging for guiding the puncture biopsy remains a challenge. In order to address this issue, a multimodality imaging and therapeutic method was developed in the present study to facilitate long-term ultrasonic and fluorescence imaging-guided precision diagnosis and combined therapy of tumors. In this regard, certain types of photoactivated gas-generating nanocontrast agents (PGNAs), capable of exhibiting both ultrasonic and fluorescence imaging ability along with photothermal and sonodynamic function, were designed and fabricated. The advantages of these fabricated PGNAs were then utilized against tumors in vivo, and high therapeutic efficacy was achieved through long-term ultrasonic imaging-guided treatment. In particular, the as-prepared multifunctional PGNAs were applied successfully for the fluorescence-based determination of patient tumor samples collected through puncture biopsy in clinics, and superior performance was observed compared to the clinically used SonoVue contrast agents that are incapable of specifically distinguishing the tumor in ex vivo tissues.

Characterization and Comparison of Contrast Imaging Properties of Naturally Isolated and Heterologously Expressed Gas Vesicles

Nanoscale ultrasound contrast agents have attracted considerable interest in the medical imaging field for their ability to penetrate tumor vasculature and enable targeted imaging of cancer cells by attaching to tumor-specific ligands. Despite their potential, traditional chemically synthesized contrast agents face challenges related to complex synthesis, poor biocompatibility, and inconsistent imaging due to non-uniform particle sizes. To address these limitations, bio-synthesized nanoscale ultrasound contrast agents have been proposed as a viable alternative, offering advantages such as enhanced biocompatibility, consistent particle size for reliable imaging, and the potential for precise functionalization to improve tumor targeting. In this study, we successfully isolated cylindrical gas vesicles (GVs) from Serratia. 39006 and subsequently introduced the GVs-encoding gene cluster into Escherichia coli using genetic engineering techniques. We then characterized the contrast imaging properties of two kinds of purified GVs, using in vitro and in vivo methods. Our results demonstrated that naturally isolated GVs could produce stable ultrasound contrast signals in murine livers and tumors using clinical diagnostic ultrasound equipment. Additionally, heterologously expressed GVs from gene-engineered bacteria also exhibited good ultrasound contrast performance. Thus, our study presents favorable support for the application of genetic engineering techniques in the modification of gas vesicles for future biomedical practice.

Sonogenetics-controlled synthetic designer cells for cancer therapy in tumor mouse models

Bacteria-based therapies are powerful strategies for cancer therapy, yet their clinical application is limited by a lack of tunable genetic switches to safely regulate the local expression and release of therapeutic cargoes. Rapid advances in remote-control technologies have enabled precise control of biological processes in time and space. We developed therapeutically active engineered bacteria mediated by a sono-activatable integrated gene circuit based on the thermosensitive transcriptional repressor TlpA39. Through promoter engineering and ribosome binding site screening, we achieved ultrasound (US)-induced protein expression and secretion in engineered bacteria with minimal noise and high induction efficiency. Specifically, delivered either intratumorally or intravenously, engineered bacteria colonizing tumors suppressed tumor growth through US-irradiation-induced release of the apoptotic protein azurin and an immune checkpoint inhibitor, a nanobody targeting programmed death-ligand 1, in different tumor mouse models. Beyond developing safe and high-performance designer bacteria for tumor therapy, our study illustrates a sonogenetics-controlled therapeutic platform that can be harnessed for bacteria-based precision medicine.

Recent Progress in Peptide-Based Molecular Probes for Disease Bioimaging

Recent strides in molecular pathology have unveiled distinctive alterations at the molecular level throughout the onset and progression of diseases. Enhancing the in vivo visualization of these biomarkers is crucial for advancing disease classification, staging, and treatment strategies. Peptide-based molecular probes (PMPs) have emerged as versatile tools due to their exceptional ability to discern these molecular changes with unparalleled specificity and precision. In this Perspective, we first summarize the methodologies for crafting innovative functional peptides, emphasizing recent advancements in both peptide library technologies and computer-assisted peptide design approaches. Furthermore, we offer an overview of the latest advances in PMPs within the realm of biological imaging, showcasing their varied applications in diagnostic and therapeutic modalities. We also briefly address current challenges and potential future directions in this dynamic field.

Phase transition of GvpU regulates gas vesicle clustering in bacteria

Gas vesicles (GVs) are microbial protein organelles that support cellular buoyancy. GV engineering has multiple applications, including reporter gene imaging, acoustic control and payload delivery. GVs often cluster into a honeycomb pattern to minimize occupancy of the cytosol. The underlying molecular mechanism and the influence on cellular physiology remain unknown. Using genetic, biochemical and imaging approaches, here we identify GvpU from Priestia megaterium as a protein that regulates GV clustering in vitro and upon expression in Escherichia coli. GvpU binds to the C-terminal tail of the core GV shell protein and undergoes a phase transition to form clusters in subsaturated solution. These properties of GvpU tune GV clustering and directly modulate bacterial fitness. GV variants can be designed with controllable sensitivity to GvpU-mediated clustering, enabling design of genetically tunable biosensors. Our findings elucidate the molecular mechanisms and functional roles of GV clustering, enabling its programmability for biomedical applications.

Sonogenetics for Monitoring and Modulating Biomolecular Function by Ultrasound

Ultrasound technology, synergistically harnessed with genetic engineering and chemistry concepts, has started to open the gateway to the remarkable realm of sonogenetics-a pioneering paradigm for remotely orchestrating cellular functions at the molecular level. This fusion not only enables precisely targeted imaging and therapeutic interventions, but also advances our comprehension of mechanobiology to unparalleled depths. Sonogenetic tools harness mechanical force within small tissue volumes while preserving the integrity of the surrounding physiological environment, reaching depths of up to tens of centimeters with high spatiotemporal precision. These capabilities circumvent the inherent physical limitations of alternative in vivo control methods such as optogenetics and magnetogenetics. In this review, we first discuss mechanosensitive ion channels, the most commonly utilized sonogenetic mediators, in both mammalian and non-mammalian systems. Subsequently, we provide a comprehensive overview of state-of-the-art sonogenetic approaches that leverage thermal or mechanical features of ultrasonic waves. Additionally, we explore strategies centered around the design of mechanochemically reactive macromolecular systems. Furthermore, we delve into the realm of ultrasound imaging of biomolecular function, encompassing the utilization of gas vesicles and acoustic reporter genes. Finally, we shed light on limitations and challenges of sonogenetics and present a perspective on the future of this promising technology.

A drug-selectable acoustic reporter gene system for human cell ultrasound imaging

A promising new field of genetically encoded ultrasound contrast agents in the form of gas vesicles has recently emerged, which could extend the specificity of medical ultrasound imaging. However, given the delicate genetic nature of how these genes are integrated and expressed, current methods of producing gas vesicle-expressing mammalian cell lines requires significant cell processing time to establish a clonal/polyclonal line that robustly expresses the gas vesicles sufficiently enough for ultrasound contrast. Here, we describe an inducible and drug-selectable acoustic reporter gene system that can enable gas vesicle expression in mammalian cell lines, which we demonstrate using HEK293T cells. Our drug-selectable construct design increases the stability and proportion of cells that successfully integrate all plasmids into their genome, thus reducing the amount of cell processing time required. Additionally, we demonstrate that our drug-selectable strategy forgoes the need for single-cell cloning and fluorescence-activated cell sorting, and that a drug-selected mixed population is sufficient to generate robust ultrasound contrast. Successful gas vesicle expression was optically and ultrasonically verified, with cells expressing gas vesicles exhibiting an 80% greater signal-to-noise ratio compared to negative controls and a 500% greater signal-to-noise ratio compared to wild-type HEK293T cells. This technology presents a new reporter gene paradigm by which ultrasound can be harnessed to visualize specific cell types for applications including cellular reporting and cell therapies.

Quantifying nanoparticle delivery: challenges, tools, and advances

This review explores challenges and methods for quantifying nanoparticle delivery in therapeutic applications. We discuss three main approaches: (1) functional readouts that assess therapeutic effects post nanoparticle administration, (2) nanocarrier tracking that directly monitors the nanoparticle localization, and (3) cargo tracking that infers nanoparticle localization by measuring encapsulated agents or attached surface tags. Reanalysis of the Wilhelm et al. Cancer Nanomedicine Repository dataset found mixed quantification methodologies, which could cause misleading conclusions. We discuss potential pitfalls in each quantification approach and highlight recent advancements in novel technologies. It is important that researchers select appropriate quantification methods based on their objectives and consider integrating multiple approaches for a comprehensive understanding of in vivo nanoparticle behavior to facilitate their clinical translation.

Exploiting Sound for Emerging Applications of Extracellular Vesicles

Extracellular vesicles are nano- to microscale, membrane-bound particles released by cells into extracellular space, and act as carriers of biomarkers and therapeutics, holding promising potential in translational medicine. However, the challenges remain in handling and detecting extracellular vesicles for disease diagnosis as well as exploring their therapeutic capability for disease treatment. Here, we review the recent engineering and technology advances by leveraging the power of sound waves to address the challenges in diagnostic and therapeutic applications of extracellular vesicles and biomimetic nanovesicles. We first introduce the fundamental principles of sound waves for understanding different acoustic-assisted extracellular vesicle technologies. We discuss the acoustic-assisted diagnostic methods including the purification, manipulation, biosensing, and bioimaging of extracellular vesicles. Then, we summarize the recent advances in acoustically enhanced therapeutics using extracellular vesicles and biomimetic nanovesicles. Finally, we provide perspectives into current challenges and future clinical applications of the promising extracellular vesicles and biomimetic nanovesicles powered by sound.

Ultrasound technology assisted colloidal nanocrystal synthesis and biomedical applications

Non-invasive and high spatiotemporal resolution mythologies for the diagnosis and treatment of disease in clinical medicine promote the development of modern medicine. Ultrasound (US) technology provides a non-invasive, real-time, and cost-effective clinical imaging modality, which plays a significant role in chemical synthesis and clinical translation, especially in in vivo imaging and cancer therapy. On the one hand, the US treatment is usually accompanied by cavitation, leading to high temperature and pressure, so-called "hot spot", playing a significant role in sonochemical-based colloidal synthesis. Compared with the classical nucleation synthetic method, the sonochemical synthesis strategy presents high efficiency for the fabrication of colloidal nanocrystals due to its fast nucleation and growth procedure. On the other hand, the US is attractive for in vivo and medical treatment, with applications increasing with the development of novel contrast agents, such as the micro and nano bubbles, which are widely used in neuromodulation, with which the US can breach the blood-brain barrier temporarily and safely, opening a new door to neuromodulation and therapy. In terms of cancer treatment, sonodynamic therapy and US-assisted synergetic therapy show great effects against cancer and sonodynamic immunotherapy present unparalleled potentiality compared with other synergetic therapies. Further development of ultrasound technology can revolutionize both chemical synthesis and clinical translation by improving efficiency, precision, and accessibility while reducing environmental impact and enhancing patient care. In this paper, we review the US-assisted sonochemical synthesis and biological applications, to promote the next generation US technology-assisted applications.

Bacteria-Based Living Probes: Preparation and the Applications in Bioimaging and Diagnosis

Bacteria can colonize a variety of in vivo biointerfaces, particularly the skin, nasal, and oral mucosa, the gastrointestinal tract, and the reproductive tract, but also target specific lesion sites, such as tumor and wound. By virtue of their prominent characteristics in motility, editability, and targeting ability, bacteria carrying imageable agents are widely developed as living probes for bioimaging and diagnosis of different diseases. This review first introduces the strategies used for preparing bacteria-based living probes, including biological engineering, chemical modification, intracellular loading, and optical manipulation. It then summarizes the recent progress of these living probes for fluorescence imaging, near-infrared imaging, ultrasonic imaging, photoacoustic imaging, magnetic resonance imaging, and positron emission tomography imaging. The biomedical applications of bacteria-based living probes are also reviewed particularly in the bioimaging and diagnosis of bacterial infections, cancers, and intestine-associated diseases. In addition, the advantages and challenges of bacteria-based living probes are discussed and future perspectives are also proposed. This review provides an updated overview of bacteria-based living probes, highlighting their great potential as a unique yet versatile platform for developing next-generation imageable agents for intelligent bioimaging, diagnosis, and even therapy.

Modulation of Point Spread Function for Super-Resolution Imaging

High image resolution is desired in wave-related areas such as ultrasound, acoustics, optics, and electromagnetics. However, the spatial resolution of an imaging system is limited by the spatial frequency of the point spread function (PSF) of the system due to diffraction. In this article, the PSF is modulated in amplitude, phase, or both to increase the spatial frequency to reconstruct super-resolution images of objects or wave sources/fields, where the modulator can be a focused shear wave produced remotely by, for example, a radiation force from a focused Bessel beam or X-wave, or can be a small particle manipulated remotely by a radiation-force (such as acoustic and optical tweezers) or electrical and magnetic forces. A theory of the PSF-modulation method was developed, and computer simulations and experiments were conducted. The result of an ultrasound experiment shows that a pulse-echo (two-way) image reconstructed has a super-resolution (0.65 mm) as compared to the diffraction limit (2.65 mm) using a 0.5-mm-diameter modulator at 1.483-mm wavelength, and the signal-to-noise ratio (SNR) of the image was about 31 dB. If the minimal SNR of a "visible" image is 3, the resolution can be further increased to about 0.19 mm by decreasing the size of the modulator. Another ultrasound experiment shows that a wave source was imaged (one-way) at about 30-dB SNR using the same modulator size and wavelength above. The image clearly separated two 0.5-mm spaced lines, which gives a 7.26-fold higher resolution than that of the diffraction limit (3.63 mm). Although, in theory, the method has no limit on the highest achievable image resolution, in practice, the resolution is limited by noises. Also, a PSF-weighted super-resolution imaging method based on the PSF-modulation method was developed. This method is easier to implement but may have some limitations. Finally, the methods above can be applied to imaging systems of an arbitrary PSF and can produce 4-D super-resolution images. With a proper choice of a modulator (e.g., a quantum dot) and imaging system, nanoscale (a few nanometers) imaging is possible.

Gas Vesicle-Blood Interactions Enhance Ultrasound Imaging Contrast

Gas vesicles (GVs) are genetically encoded, air-filled protein nanostructures of broad interest for biomedical research and clinical applications, acting as imaging and therapeutic agents for ultrasound, magnetic resonance, and optical techniques. However, the biomedical applications of GVs as systemically injectable nanomaterials have been hindered by a lack of understanding of GVs' interactions with blood components, which can significantly impact in vivo behavior. Here, we investigate the dynamics of GVs in the bloodstream using a combination of ultrasound and optical imaging, surface functionalization, flow cytometry, and mass spectrometry. We find that erythrocytes and serum proteins bind to GVs and shape their acoustic response, circulation time, and immunogenicity. We show that by modifying the GV surface we can alter these interactions and thereby modify GVs' in vivo performance. These results provide critical insights for the development of GVs as agents for nanomedicine.

Engineered live bacteria as disease detection and diagnosis tools

Sensitive and minimally invasive medical diagnostics are essential to the early detection of diseases, monitoring their progression and response to treatment. Engineered bacteria as live sensors are being developed as a new class of biosensors for sensitive, robust, noninvasive, and in situ detection of disease onset at low cost. Akin to microrobotic systems, a combination of simple genetic rules, basic logic gates, and complex synthetic bioengineering principles are used to program bacterial vectors as living machines for detecting biomarkers of diseases, some of which cannot be detected with other sensing technologies. Bacterial whole-cell biosensors (BWCBs) can have wide-ranging functions from detection only, to detection and recording, to closed-loop detection-regulated treatment. In this review article, we first summarize the unique benefits of bacteria as living sensors. We then describe the different bacteria-based diagnosis approaches and provide examples of diagnosing various diseases and disorders. We also discuss the use of bacteria as imaging vectors for disease detection and image-guided surgery. We conclude by highlighting current challenges and opportunities for further exploration toward clinical translation of these bacteria-based systems.

Tracking adoptive natural killer cells via ultrasound imaging assisted with nanobubbles

The recent years has witnessed an exponential growth in the field of natural killer (NK) cell-based immunotherapy for cancer treatment. As a prerequisite to precise evaluations and on-demand interventions, the noninvasive tracking of adoptive NK cells plays a crucial role not only in post-treatment monitoring, but also in offering opportunities for preclinical studies on therapy optimizations. Here, we describe an NK cell tracking strategy for cancer immunotherapy based on ultrasound imaging modality. Nanosized ultrasound contrast agents, gas vesicles (GVs), were surface-functionalized to label NK cells. Unlike traditional microbubble contrast agents, nanosized GVs with their unique thermodynamical stability enable the detection of labeled NK cells under nonlinear contrast-enhanced ultrasound (nCEUS), without a noticeable impact on cellular viability or migration. By such labeling, we were able to monitor the trafficking of systematically infused NK cells to a subcutaneous tumor model. Upon co-treatment with interleukin (IL)-2, we observed a rapid enhancement in NK cell trafficking at the tumor site as early as 3 h post-infusion. Altogether, we show that the proposed ultrasound-based tracking strategy is able to capture the dynamical changes of cell trafficking in NK cell-based immunotherapy, providing referencing information for early-phase monotherapy evaluation, as well as understanding the effects of modulatory co-treatment. STATEMENT OF SIGNIFICANCE: In cellular immunotherapies, the post-infusion monitoring of the living therapeutics has been challenging. Several popular imaging modalities have been explored the monitoring of the adoptive immune cells, evaluating their trafficking and accumulation in the tumor. Here we demonstrated, for the first time, the ultrasound imaging-based immune cell tracking strategy. We showed that the acoustic labeling of adoptive immune cells was feasible with nanosized ultrasound contrast agents, overcoming the size and stability limitations of traditional microbubbles, enabling dynamical tracking of adoptive natural killer cells in both monotherapy and synergic treatment with cytokines. This article introduced the cost-effective and ubiquitous ultrasound imaging modality into the field of cellular immunotherapies, with broad prospectives in early assessment and on-demand image-guided interventions.

Gas vesicle-blood interactions enhance ultrasound imaging contrast

Gas vesicles (GVs) are genetically encoded, air-filled protein nanostructures of broad interest for biomedical research and clinical applications, acting as imaging and therapeutic agents for ultrasound, magnetic resonance, and optical techniques. However, the biomedical applications of GVs as a systemically injectable nanomaterial have been hindered by a lack of understanding of GVs' interactions with blood components, which can significantly impact in vivo performance. Here, we investigate the dynamics of GVs in the bloodstream using a combination of ultrasound and optical imaging, surface functionalization, flow cytometry, and mass spectrometry. We find that erythrocytes and serum proteins bind to GVs and shape their acoustic response, circulation time, and immunogenicity. We show that by modifying the GV surface, we can alter these interactions and thereby modify GVs' in vivo performance. These results provide critical insights for the development of GVs as agents for nanomedicine.

50-nm gas-filled protein nanostructures to enable the access of lymphatic cells by ultrasound technologies

Ultrasound imaging and ultrasound-mediated gene and drug delivery are rapidly advancing diagnostic and therapeutic methods; however, their use is often limited by the need of microbubbles, which cannot transverse many biological barriers due to their large size. Here we introduce 50-nm gas-filled protein nanostructures derived from genetically engineered gas vesicles that we referred to as 50nm GVs. These diamond-shaped nanostructures have hydrodynamic diameters smaller than commercially available 50-nm gold nanoparticles and are, to our knowledge, the smallest stable, free-floating bubbles made to date. 50nm GVs can be produced in bacteria, purified through centrifugation, and remain stable for months. Interstitially injected 50nm GVs can extravasate into lymphatic tissues and gain access to critical immune cell populations, and electron microscopy images of lymph node tissues reveal their subcellular location in antigen-presenting cells adjacent to lymphocytes. We anticipate that 50nm GVs can substantially broaden the range of cells accessible to current ultrasound technologies and may generate applications beyond biomedicine as ultrasmall stable gas-filled nanomaterials.

Truly tiny acoustic biomolecules for ultrasound imaging and therapy

Nanotechnology offers significant advantages for medical imaging and therapy, including enhanced contrast and precision targeting. However, integrating these benefits into ultrasonography has been challenging due to the size and stability constraints of conventional bubble-based agents. Here we describe bicones, truly tiny acoustic contrast agents based on gas vesicles, a unique class of air-filled protein nanostructures naturally produced in buoyant microbes. We show that these sub-80 nm particles can be effectively detected both in vitro and in vivo, infiltrate tumors via leaky vasculature, deliver potent mechanical effects through ultrasound-induced inertial cavitation, and are easily engineered for molecular targeting, prolonged circulation time, and payload conjugation.

Fluorescence, ultrasonic and photoacoustic imaging for analysis and diagnosis of diseases

Biomedical imaging technology, which allows us to peer deeply within living subjects and visually explore the delivery and distribution of agents in living things, is producing tremendous opportunities for the early diagnosis and precise therapy of diseases. In this feature article, based on reviewing the latest representative examples of progress together with our recent efforts in the bioimaging field, we intend to introduce three typical kinds of non-invasive imaging technologies, i.e., fluorescence, ultrasonic and photoacoustic imaging, in which optical and/or acoustic signals are employed for analyzing various diseases. In particular, fluorescence imaging possesses a series of outstanding advantages, such as high temporal resolution, as well as rapid and sensitive feedback. Hence, in the first section, we will introduce the latest studies on developing novel fluorescence imaging methods for imaging bacterial infections, cancer and lymph node metastasis in a long-term and real-time manner. However, the issues of imaging penetration depth induced by photon scattering and light attenuation of biological tissue limit their widespread in vivo imaging applications. Taking advantage of the excellect penetration depth of acoustic signals, ultrasonic imaging has been widely applied for determining the location, size and shape of organs, identifying normal and abnormal tissues, as well as confirming the edges of lesions in hospitals. Thus, in the second section, we will briefly summarize recent advances in ultrasonic imaging techniques for diagnosing diseases in deep tissues. Nevertheless, the absence of lesion targeting and dependency on a professional technician may lead to the possibility of false-positive diagnosis. By combining the merits of both optical and acoustic signals, newly-developed photoacoustic imaging, simultaneously featuring higher temporal and spatial resolution with good sensitivity, as well as deeper penetration depth, is discussed in the third secretion. In the final part, we further discuss the major challenges and prospects for developing imaging technology for accurate disease diagnosis. We believe that these non-invasive imaging technologies will introduce a new perspective for the precise diagnosis of various diseases in the future.

Ultrasound contrast agents from microbubbles to biogenic gas vesicles

Microbubbles have been the earliest and most widely used ultrasound contrast agents by virtue of their unique features: such as non-toxicity, intravenous injectability, ability to cross the pulmonary capillary bed, and significant enhancement of echo signals for the duration of the examination, resulting in essential preclinical and clinical applications. The use of microbubbles functionalized with targeting ligands to bind to specific targets in the bloodstream has further enabled ultrasound molecular imaging. Nevertheless, it is very challenging to utilize targeted microbubbles for molecular imaging of extravascular targets due to their size. A series of acoustic nanomaterials have been developed for breaking free from this constraint. Especially, biogenic gas vesicles, gas-filled protein nanostructures from microorganisms, were engineered as the first biomolecular ultrasound contrast agents, opening the door for more direct visualization of cellular and molecular function by ultrasound imaging. The ordered protein shell structure and unique gas filling mechanism of biogenic gas vesicles endow them with excellent stability and attractive acoustic responses. What's more, their genetic encodability enables them to act as acoustic reporter genes. This article reviews the upgrading progresses of ultrasound contrast agents from microbubbles to biogenic gas vesicles, and the opportunities and challenges for the commercial and clinical translation of the nascent field of biomolecular ultrasound.

Integration of microlenses on surface-micromachined optical ultrasound transducer array to improve detection sensitivity for parallel data readout

This Letter reports the integration of microlenses (MLs) on a surface-micromachined optical ultrasound transducer (SMOUT) array to enable parallel ultrasound data readout from a multiplicity of elements. The MLs are fabricated by photoresist patterning and reflow, and their focal lengths are optimized with parametric studies. Experiments are conducted to characterize the acoustic responsivity and its uniformity of the SMOUT-ML elements under different conditions. The temporal stability of SMOUT-ML elements immersed in water is assessed by monitoring their acoustic response continuously for 1 week. Parallel ultrasound signal readout is simulated with a small group of SMOUT-ML elements. Experimental results show that high acoustic sensitivity and excellent long-term stability can be achieved by the ML-integrated SMOUT array, which could provide a promising approach for enabling parallel ultrasound data acquisition for improving the imaging speed of 3D acoustic tomography.

Genomically mined acoustic reporter genes for real-time in vivo monitoring of tumors and tumor-homing bacteria

Ultrasound allows imaging at a much greater depth than optical methods, but existing genetically encoded acoustic reporters for in vivo cellular imaging have been limited by poor sensitivity, specificity and in vivo expression. Here we describe two acoustic reporter genes (ARGs)-one for use in bacteria and one for use in mammalian cells-identified through a phylogenetic screen of candidate gas vesicle gene clusters from diverse bacteria and archaea that provide stronger ultrasound contrast, produce non-linear signals distinguishable from background tissue and have stable long-term expression. Compared to their first-generation counterparts, these improved bacterial and mammalian ARGs produce 9-fold and 38-fold stronger non-linear contrast, respectively. Using these new ARGs, we non-invasively imaged in situ tumor colonization and gene expression in tumor-homing therapeutic bacteria, tracked the progression of tumor gene expression and growth in a mouse model of breast cancer, and performed gene-expression-guided needle biopsies of a genetically mosaic tumor, demonstrating non-invasive access to dynamic biological processes at centimeter depth.

Ultrasound Molecular Imaging and Its Applications in Cancer Diagnosis and Therapy

Ultrasound imaging is regarded as a highly sensitive imaging modality used in routine clinical examinations. Over the last several decades, ultrasound contrast agents have been widely applied in ultrasound molecular cancer imaging to improve the detection, characterization, and quantification of tumors. To date, a few new potential preclinical and clinical applications regarding ultrasound molecular cancer imaging are being investigated. This review presents an overview of the various kinds of ultrasound contrast agents employed in ultrasound molecular imaging and advanced imaging techniques using these contrast agents. Additionally, we discuss the recent enormous development of ultrasound contrast agents in the relevant preclinical and clinical applications, highlight the recent challenges which need to be overcome to accelerate the clinical translation, and discuss the future perspective of ultrasound molecular cancer imaging using various contrast agents. As a highly promising and valuable tumor-specific imaging technique, it is believed that ultrasound molecular imaging will pave an accurate and efficient way for cancer diagnosis.

Cybergenetic control of microbial community composition

The use of bacterial communities in bioproduction instead of monocultures has potential advantages including increased productivity through division of labour, ability to utilise cheaper substrates, and robustness against perturbations. A key challenge in the application of engineered bacterial communities is the ability to reliably control the composition of the community in terms of its constituent species. This is crucial to prevent faster growing species from outcompeting others with a lower relative fitness, and to ensure that all species are present at an optimal ratio during different steps in a biotechnological process. In contrast to purely biological approaches such as synthetic quorum sensing circuits or paired auxotrophies, cybergenetic control techniques - those in which computers interface with living cells-are emerging as an alternative approach with many advantages. The community composition is measured through methods such as fluorescence intensity or flow cytometry, with measured data fed real-time into a computer. A control action is computed using a variety of possible control algorithms and then applied to the system, with actuation taking the form of chemical (e.g., inducers, nutrients) or physical (e.g., optogenetic, mechanical) inputs. Subsequent changes in composition are then measured and the cycle repeated, maintaining or driving the system to a desired state. This review discusses recent and future developments in methods for implementing cybergenetic control systems, contrasts their capabilities with those of traditional biological methods of population control, and discusses future directions and outstanding challenges for the field.

Genetic Circuit Design in Rhizobacteria

Genetically engineered plants hold enormous promise for tackling global food security and agricultural sustainability challenges. However, construction of plant-based genetic circuitry is constrained by a lack of well-characterized genetic parts and circuit design rules. In contrast, advances in bacterial synthetic biology have yielded a wealth of sensors, actuators, and other tools that can be used to build bacterial circuitry. As root-colonizing bacteria (rhizobacteria) exert substantial influence over plant health and growth, genetic circuit design in these microorganisms can be used to indirectly engineer plants and accelerate the design-build-test-learn cycle. Here, we outline genetic parts and best practices for designing rhizobacterial circuits, with an emphasis on sensors, actuators, and chassis species that can be used to monitor/control rhizosphere and plant processes.

Molecular imaging approaches to facilitate bacteria-mediated cancer therapy

Bacteria-mediated cancer therapy is a potential therapeutic strategy for cancer that has unique properties, including broad tumor-targeting ability, various administration routes, the flexibility of delivery, and facilitating the host's immune responses. The molecular imaging of bacteria-mediated cancer therapy allows the therapeutically injected bacteria to be visualized and confirms the accurate delivery of the therapeutic bacteria to the target lesion. Several hurdles make bacteria-specific imaging challenging, including the need to discriminate therapeutic bacterial infection from inflammation or other pathologic lesions. To realize the full potential of bacteria-specific imaging, it is necessary to develop bacteria-specific targets that can be associated with an imaging assay. This review describes the current status of bacterial imaging techniques together with the advantages and disadvantages of several imaging modalities. Also, we describe potential targets for bacterial-specific imaging and related applications.

Nanoengineered Neutrophils as a Cellular Sonosensitizer for Visual Sonodynamic Therapy of Malignant Tumors

The rapid evolution of cell-based theranostics has attracted extensive attention due to their unique advantages in biomedical applications. However, the inherent functions of cells alone cannot meet the needs of malignant tumor treatment. Thus endowing original cells with new characteristics to generate multifunctional living cells may hold a tremendous promise. Here, the nanoengineering method is used to combine customized liposomes with neutrophils, generating oxygen-carrying sonosensitizer cells with acoustic functions, which are called Acouscyte/O₂ , for the visual diagnosis and treatment of cancer. Specifically, oxygen-carried perfluorocarbon and temoporfin are encapsulated into cRGD peptide modified multilayer liposomes (C-ML/HPT/O₂ ), which are then loaded into live neutrophils to obtain Acouscyte/O₂ . Acouscyte/O₂ can not only carry a large amount of oxygen but also exhibits the ability of long circulation, inflammation-triggered recruitment, and decomposition. Importantly, Acouscyte/O₂ can be selectively accumulated in tumors, effectively enhancing tumor oxygen levels, and triggering anticancer sonodynamics in response to ultrasound stimulation, leading to complete obliteration of tumors and efficient extension of the survival time of tumor-bearing mice with minimal systemic adverse effects. Meanwhile, the tumors can be monitored in real time by temoporfin-mediated fluorescence imaging and perfluorocarbon (PFC)-microbubble-enhanced ultrasound imaging. Therefore, the nanoengineered neutrophils, i.e., Acouscyte/O₂ , are a new type of multifunctional cellular drug, which provides a new platform for the diagnosis and sonodynamic therapy of solid malignant tumors.

New Insights for Biosensing: Lessons from Microbial Defense Systems

Microorganisms have gained defense systems during the lengthy process of evolution over millions of years. Such defense systems can protect them from being attacked by invading species (e.g., CRISPR-Cas for establishing adaptive immune systems and nanopore-forming toxins as virulence factors) or enable them to adapt to different conditions (e.g., gas vesicles for achieving buoyancy control). These microorganism defense systems (MDS) have inspired the development of biosensors that have received much attention in a wide range of fields including life science research, food safety, and medical diagnosis. This Review comprehensively analyzes biosensing platforms originating from MDS for sensing and imaging biological analytes. We first describe a basic overview of MDS and MDS-inspired biosensing platforms (e.g., CRISPR-Cas systems, nanopore-forming proteins, and gas vesicles), followed by a critical discussion of their functions and properties. We then discuss several transduction mechanisms (optical, acoustic, magnetic, and electrical) involved in MDS-inspired biosensing. We further detail the applications of the MDS-inspired biosensors to detect a variety of analytes (nucleic acids, peptides, proteins, pathogens, cells, small molecules, and metal ions). In the end, we propose the key challenges and future perspectives in seeking new and improved MDS tools that can potentially lead to breakthrough discoveries in developing a new generation of biosensors with a combination of low cost; high sensitivity, accuracy, and precision; and fast detection. Overall, this Review gives a historical review of MDS, elucidates the principles of emulating MDS to develop biosensors, and analyzes the recent advancements, current challenges, and future trends in this field. It provides a unique critical analysis of emulating MDS to develop robust biosensors and discusses the design of such biosensors using elements found in MDS, showing that emulating MDS is a promising approach to conceptually advancing the design of biosensors.