Maltotriose-based probes for fluorescence and photoacoustic imaging of bacterial infections

Conceptually innovative fluorophores for functional bioimaging

Fluorophore chemistry is at the forefront of bioimaging, revolutionizing the visualization of biological processes with unparalleled precision. From the serendipitous discovery of mauveine in 1856 to cutting-edge fluorophore engineering, this field has undergone transformative evolution. Today, the synergy of chemistry, biology, and imaging technologies has produced diverse, specialized fluorophores that enhance brightness, photostability, and targeting capabilities. This review delves into the history and innovation of fluorescent probes, showcasing their pivotal role in advancing our understanding of cellular dynamics and disease mechanisms. We highlight groundbreaking molecules and their applications, envisioning future breakthroughs that promise to redefine biomedical research and diagnostics.

Local Release of Copper Manganese Oxide Using HA Microneedle for Improving the Efficacy of Drug-Resistant Wound Inflammation

The production of bacterial toxins and excessive accumulation of reactive oxygen species (ROS) can induce localized oxidative stress, triggering an exaggerated immune response that impedes wound healing and culminates in chronic wounds. To address this issue, a microneedle (MN) system loaded with copper-manganese oxide (CMO) is developed to modulate the hyperimmune response in wounds. CMO@MN exhibits excellent antimicrobial and anti-inflammatory properties by effectively killing bacteria, scavenging ROS, and modulating macrophage polarization through their multiple enzymatic activities and photothermal properties. RNA sequencing revealed that CMO@MN improved the therapeutic effect on the infected skin of mice by balancing the ratio of M1/M2 macrophages and promoting cell migration and angiogenesis through the regulation of relevant pathways. Overall, this CMO@MN patch skillfully balances the complex issues between the immune response and wound healing and has potential applications in the treatment of other serious bacterial infections.

Versatile self-assembled near-infrared SERS nanoprobes for multidrug-resistant bacterial infection-specific surveillance and therapy

The rise of multidrug-resistant bacteria (MDRB) has made bacterial infection one of the biggest health threats, causing numerous antibiotics to fail. Real-time monitoring of bacterial disease treatment efficacy at the infection site is required. Herein, we report a versatile Raman tag 3,3'-diethylthiatricarbocyanine iodide (DTTC)-conjugated star-shaped Au-MoS2@hyaluronic acid (AMD@HA) nanocomposite as a surface-enhanced Raman scattering (SERS) nanoprobe for quick bacterial identification and in-situ eradication. Localized surface plasmon resonance (LSPR) from the hybrid metallic nanostructure makes AMD@HA highly responsive to the near-infrared laser, enabling it to demonstrate a photothermal (PTT) effect, increased SERS activity, and peroxidase-like catalytic reaction to release reactive oxygen species. The tail vein injection of AMD@HA nanoprobes is invasive, however SERS imaging for bacterial identification is non-invasive and sensitive, making it an efficient residual bacteria monitoring method. The detection limit for methicillin-resistant Staphylococcus aureus (MRSA) is as low as 102 CFU·mL-1, and the substrates allow for taking 120 s to acquire a Raman image of 1600 (40 × 40) pixels. In mouse models of MRSA-induced wound infection and skin abscess, the combination of AMD@HA-mediated PTT and catalytic therapy demonstrates a synergistic effect in promoting wound healing through rapid sterilization. This SERS-guided therapeutic approach exhibits little toxicity and does not cause considerable collateral damage, offering a highly promising intervention for treating diseases caused by MDRB. STATEMENT OF SIGNIFICANCE: This research introduces a SERS nanoprobe, AMD@HA, for the rapid identification and eradication of multidrug-resistant bacteria (MDRB), a critical health threat. The nanoprobe leverages localized surface plasmon resonance for photothermal therapy and enhanced Raman signals, offering a sensitive, non-invasive diagnostic tool. With a low detection limit for MRSA and a synergistic therapeutic effect in mouse models, our approach holds significant promise for treating MDRB-driven infections with minimal toxicity, advancing the field of antimicrobial strategies.

Click-free imaging of carbohydrate trafficking in live cells using an azido photothermal probe

Real-time tracking of intracellular carbohydrates remains challenging. While click chemistry allows bio-orthogonal tagging with fluorescent probes, the reaction permanently alters the target molecule and only allows a single snapshot. Here, we demonstrate click-free mid-infrared photothermal (MIP) imaging of azide-tagged carbohydrates in live cells. Leveraging the micromolar detection sensitivity for 6-azido-trehalose (TreAz) and the 300-nm spatial resolution of MIP imaging, the trehalose recycling pathway in single mycobacteria, from cytoplasmic uptake to membrane localization, is directly visualized. A peak shift of azide in MIP spectrum further uncovers interactions between TreAz and intracellular protein. MIP mapping of unreacted azide after click reaction reveals click chemistry heterogeneity within a bacterium. Broader applications of azido photothermal probes to visualize the initial steps of the Leloir pathway in yeasts and the newly synthesized glycans in mammalian cells are demonstrated.

Microbe-material hybrids for therapeutic applications

As natural living substances, microorganisms have emerged as useful resources in medicine for creating microbe-material hybrids ranging from nano to macro dimensions. The engineering of microbe-involved nanomedicine capitalizes on the distinctive physiological attributes of microbes, particularly their intrinsic "living" properties such as hypoxia tendency and oxygen production capabilities. Exploiting these remarkable characteristics in combination with other functional materials or molecules enables synergistic enhancements that hold tremendous promise for improved drug delivery, site-specific therapy, and enhanced monitoring of treatment outcomes, presenting substantial opportunities for amplifying the efficacy of disease treatments. This comprehensive review outlines the microorganisms and microbial derivatives used in biomedicine and their specific advantages for therapeutic application. In addition, we delineate the fundamental strategies and mechanisms employed for constructing microbe-material hybrids. The diverse biomedical applications of the constructed microbe-material hybrids, encompassing bioimaging, anti-tumor, anti-bacteria, anti-inflammation and other diseases therapy are exhaustively illustrated. We also discuss the current challenges and prospects associated with the clinical translation of microbe-material hybrid platforms. Therefore, the unique versatility and potential exhibited by microbe-material hybrids position them as promising candidates for the development of next-generation nanomedicine and biomaterials with unique theranostic properties and functionalities.

Synthesis of Coumarin-Based Photosensitizers for Enhanced Antibacterial Type I/II Photodynamic Therapy

Photodynamic therapy (PDT) is an effective method for treating microbial infections by leveraging the unique photophysical properties of photosensitizing agents, but issues such as fluorescence quenching and the restricted generation of reactive oxygen species (ROS) under hypoxic conditions still remain. In this study, we successfully synthesized and designed a coumarin-based aggregation-induced emission luminogen (AIEgen), called ICM, that shows a remarkable capacity for type I ROS and type II ROS generation. The 1O2 yield of ICM is 0.839. The ROS it produces include hydroxyl radicals (HO•) and superoxide anions (O2•-), with highly effective antibacterial properties specifically targeting Staphylococcus aureus (a Gram-positive bacterium). Furthermore, ICM enables broad-spectrum fluorescence imaging and exhibits excellent biocompatibility. Consequently, ICM, as a potent type I photosensitizer for eliminating pathogenic microorganisms, represents a promising tool in addressing the threat posed by these pathogens.

Photoacoustic imaging of a cyanine dye targeting bacterial infection

The development of a non-invasive infection-specific diagnostic probe holds the potential to vastly improve early-stage detection of infection, enabling precise therapeutic intervention and potentially reducing the incidence of antibiotic resistance. Towards this goal, a commercially available bacteria-targeting Zinc(II)-dipicolylamine (ZnDPA)-derived fluorophore, PSVue794, was assessed as a photoacoustic (PA) imaging probe (PIP). A radiolabeled version of the dye, [99mTc]Tc-PSVue794, was developed to facilitate quantitative biodistribution studies beyond optical imaging methods, which showed a target-to-non-target ratio of 10.1 ± 1.1, 12 h post-injection. The ability of the PIP to differentiate between bacterial infection, sterile inflammation, and healthy tissue in a mouse model, was then evaluated via PA imaging. The PA signal in sites of sterile inflammation (0.062 ± 0.012 a.u.) was not statistically different from that of the background (0.058 ± 0.006 a.u.). In contrast, high PA signal was detected at sites of bacterial infection (0.176 ± 0.011 a.u.) as compared to background (0.081 ± 0.04 a.u., where P ≤ 0.03). This work demonstrates the potential of utilizing established fluorophores towards PAI and utilizing PAI as a modality in the distinction of bacterial infection from sites of sterile inflammation.

Bridging the Translation of ICG-1-Maltotriose: A Multimodal Sensor for Monitoring and Detecting Bacterial Infections

Bacterial infections lack reliable, specific, and quick detection methods, which incur substantial costs to patients and caretakers. Our team conjugated the FDA-approved fluorescent dye indocyanine green (ICG) with a maltotriose sugar, resulting in two highly specific imaging agents (ICG-DBCO-1-Maltotriose and ICG-Amide-1-Maltotriose) for detecting bacterial infections. We then evaluated the two derivatives using fluorescence imaging (FLI), bioluminescence imaging (BLI), and photoacoustic imaging (PAI) in bacterial infection murine models. Our findings indicate that both imaging agents can correlate with and reliably detect the infection site using FLI and PAI for both Gram-negative and Gram-positive strains, with various bacterial loads. Furthermore, the differences in pharmacokinetic (PK) properties between the two agents allow for one to be used for immediate imaging (2-4 h postinjection), while the other is more effective for longitudinal studies (18-40 h postinjection).

Injectable and Near-Infrared Light-Controllable Fibrin Hydrogels with Antimicrobial and Immunomodulating Properties for Infected Wound Healing

The management of infected wounds poses a significant challenge due to the growing issue of antibiotic resistance, underscoring the urgent necessity to innovate and implement alternative therapeutic strategies. These strategies should be capable of eliminating bacterial infections in infected wounds while circumventing the induction of multi-drug resistance. In the current study, we developed an easily prepared and injectable fibrin gel (FG) loaded with nanoparticles (NPs) that exhibit antibacterial and immunomodulatory properties to facilitate the healing of infected wounds. Initially, a novel type of NP was generated through the electrostatic interaction between the photothermal agent, mPEG-modified polydopamine (MPDA), and the nitric oxide (NO) donor, S-nitrosocysteamine (SNO). This interaction resulted in the formation of NPs referred to as SNO-loaded MPDA (SMPDA). Subsequently, the SMPDA was encapsulated into the FG using a double-barreled syringe, thereby producing the SMPDA-loaded FG (SMPDA/G). Experimental results revealed that SMPDA/G could effectively eliminate bacterial infections and alter the immune microenvironment. This efficacy is attributed to the synergistic combination of NO therapy and photothermal therapy, along with the role of SMPDA in facilitating M2 macrophage polarization within the gel. Accordingly, these findings suggest that the SMPDA/G holds substantial promise for clinical application in infected wound healing.

Multimodal optoacoustic imaging: methods and contrast materials

Optoacoustic (OA) imaging offers powerful capabilities for interrogating biological tissues with rich optical absorption contrast while maintaining high spatial resolution for deep tissue observations. The spectrally distinct absorption of visible and near-infrared photons by endogenous tissue chromophores facilitates extraction of diverse anatomic, functional, molecular, and metabolic information from living tissues across various scales, from organelles and cells to whole organs and organisms. The primarily blood-related contrast and limited penetration depth of OA imaging have fostered the development of multimodal approaches to fully exploit the unique advantages and complementarity of the method. We review the recent hybridization efforts, including multimodal combinations of OA with ultrasound, fluorescence, optical coherence tomography, Raman scattering microscopy and magnetic resonance imaging as well as ionizing methods, such as X-ray computed tomography, single-photon-emission computed tomography and positron emission tomography. Considering that most molecules absorb light across a broad range of the electromagnetic spectrum, the OA interrogations can be extended to a large number of exogenously administered small molecules, particulate agents, and genetically encoded labels. This unique property further makes contrast moieties used in other imaging modalities amenable for OA sensing.

A Dual-Mode Near-Infrared Optical and Photoacoustic Imaging Agent Based on a Low Energy Absorbing Ytterbium Complex

Near-infrared (NIR) luminescence and photoacoustic (PA) imaging have attracted increasing attention for the real-time monitoring of biological samples due to high sensitivity, resolution, and pronounced signal detection depth, respectively. For improved contrast, both techniques require imaging agents possessing high absorption in the red-NIR range. Herein, we took advantage of a ternary complex formed with the anionic ytterbium(III) tetrakis(2-thenoyltrifluoroacetonate) ([Yb(tta)4]-) and the cationic NIR-absorbing chromophore, 1,1'-diethyl-2,2'-dicarbocyanine (Cy+), to evaluate its potential to act as a dual-mode NIR luminescence and PA imaging agent. We demonstrated that, upon excitation with red-NIR light, Cy[Yb(tta)4] encapsulated into polystyrene nanoparticles is able to generate both NIR Yb3+ emission and a PA signal in an imaging experiment performed in a tissue-mimicking phantom.

Click-free imaging of carbohydrate trafficking in live cells using an azido photothermal probe

Real-time tracking of intracellular carbohydrates remains challenging. While click chemistry allows bio-orthogonal tagging with fluorescent probes, the reaction permanently alters the target molecule and only allows a single snapshot. Here, we demonstrate click-free mid-infrared photothermal (MIP) imaging of azide-tagged carbohydrates in live cells. Leveraging the micromolar detection sensitivity for 6-azido-trehalose (TreAz) and the 300-nm spatial resolution of MIP imaging, the trehalose recycling pathway in single mycobacteria, from cytoplasmic uptake to membrane localization, is directly visualized. A peak shift of azide in MIP spectrum further uncovers interactions between TreAz and intracellular protein. MIP mapping of unreacted azide after click reaction reveals click chemistry heterogeneity within a bacterium. Broader applications of azido photothermal probes to visualize the initial steps of the Leloir pathway in yeasts and the newly synthesized glycans in mammalian cells are demonstrated.

Maltose-Derivatized Fluorescence Turn-On Imaging Probe for Bacteria Detection

We report a maltose-derivatized fluorescence turn-on imaging probe, Mal-Cz, to detect E. coli and Staphylococci. The fluorescence turn-on is achieved through an intramolecular C-H insertion reaction of the perfluoroaryl azide-functionalized carbazole to give a fluorescent product. Confocal fluorescence microscopy confirmed the successful uptake of Mal-Cz by E. coli and Staphylococci upon photoactivation. The Mal-Cz probe could selectively detect E. coli and S. epidermidis in the presence of P. aeruginosa and M. smegmatis without interference from these bacteria. Both the photoactivation and bacteria detection can be accomplished using a hand-held UV lamp at 365 nm, with the limit of detection of 103 CFU/mL by the naked eye. Mal-Cz could also be used to detect E. coli and S. epidermidis spiked in milk by the naked eye under a hand-held UV lamp. The uptake of Mal-Cz requires metabolically active bacteria: the uptake was reduced in stationary phase bacteria and was diminished in bacteria that were killed by heating or treating with antibiotics or sodium azide. The uptake decreased with increasing concentration of added free maltose, indicating that Mal-Cz hijacked the maltose uptake pathways. In E. coli, the maltose transport systems, including maltoporin LamB, maltose binding protein MBP, and the maltose ATP binding cassette (ABC) transporter MalFGK2, are all critical for the transport of Mal-Cz. The uptake was diminished in the deletion mutants ΔLamB, ΔMalE, ΔMalF, and ΔMalK.

Motion Rejection and Spectral Unmixing for Accurate Estimation of In Vivo Oxygen Saturation Using Multispectral Optoacoustic Tomography

Multispectral optoacoustic tomography (MSOT) uniquely enables spatial mapping in high resolution of oxygen saturation (SO2), with potential applications in studying pathological complications and therapy efficacy. MSOT offers seamless integration with ultrasonography, by using a common ultrasound (US) detector array. However, MSOT relies on multiple successive acquisitions of optoacoustic (OA) images at different optical wavelengths and the low frame rate of OA imaging makes the MSOT acquisition sensitive to body/respiratory motion. Moreover, the estimation of SO2 is highly sensitive to noise, and artifacts related to the respiratory motion of the animal were identified as the primary source of noise in MSOT. In this work, we propose a two-step image processing method for SO2 estimation in deep tissues. First, to mitigate motion artifacts, we propose a method of selection of OA images acquired only during the respiratory pause of the animal, using ultrafast ultrasound (US) images acquired immediately after each OA acquisition (US image acquisition duration of 1.4 ms and a total delay of 7 ms). We show that gating is more effective using US images than OA images at different optical wavelengths. Second, we propose a novel method that can estimate directly the SO2 value of a pixel and at the same time evaluate the amount of noise present in that pixel. Hence, the method can efficiently eliminate the pixels dominated by noise from the final SO2 map. Our postprocessing method is shown to outperform conventional methods for SO2 estimation, and the method was validated by in vivo oxygen challenge experiments.

In Situ Photoacoustic Visualization of Pneumonia Induced by MRSA and Specific Identifying Tumor-Homing Bacteria

Optical imaging holds great promise for monitoring bacterial infectious processes and drug resistance with high temporal-spatial resolution. Currently, the diagnosis of deep-seated bacterial infections in vivo with fluorescence imaging, including near-infrared (NIR) fluorescence imaging technology, remains a significant challenge due to its limited tissue penetration depth. In this study, we developed a highly specific targeting probe, Cy7-Neo-NO2, by conjugating a bacterial 16S rRNA-targeted moiety, neomycin, with a bacterial nitroreductase (NTR)-activated NIR photoacoustic (PA) scaffold using our previously developed caged photoinduced electron transfer (a-PeT) approach. This conjugation effectively resolved probe aggregation issues in physiological conditions and substantially enhanced its reactivity toward bacterial NTR. Notably, Cy7-Neo-NO2 enabled the first in situ photoacoustic imaging of pneumonia induced by methicillin-resistant Staphylococcus aureus (MRSA), as well as the detection of bacteria within tumors. Furthermore, upon NIR irradiation, Cy7-Neo-NO2 successfully inhibited MRSA growth through a synergistic effect combining photothermal therapy and photodynamic therapy. Our results provided an effective tool for obtaining exceptional PA agents for accurate diagnosis, therapeutic evaluation of deep-seated bacterial infections in vivo, and intratumoral bacteria-specific recognition.

Advances in Optical Probes for the Detection of Hydrazine in Environmental and Biological Systems

Hydrazine, as a crucial raw material in the fine chemical industry, plays an indispensable role in fuel, catalyst, pesticide and drug synthesis. Due to its good water solubility and high toxicity, hydrazine can cause irreparable damage to water and soil in the environment, and it can also be released by taking certain drugs, which brings potential risks to human health. Therefore, it is vital to develop a method that can specifically detect hydrazine in the environment and in vivo. As an effective analysis and detection tool, fluorescence probe has attracted extensive attention in recent years. In this review, we summarized and classified hydrazine fluorescence probes based on various reaction mechanisms, and discussed their structures and applications in the past ten years. At least, we briefly outline the challenges and prospects in this field.

The Promise of Molecular Imaging: Focus on Central Nervous System Infections

Central nervous system (CNS) infections can lead to high mortality and severe morbidity. Diagnosis, monitoring, and assessing response to therapy of CNS infections is particularly challenging with traditional tools, such as microbiology, due to the dangers associated with invasive CNS procedures (ie, biopsy or surgical resection) to obtain tissues. Molecular imaging techniques like positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging have long been used to complement anatomic imaging such as computed tomography (CT) and magnetic resonance imaging (MRI), for in vivo evaluation of disease pathophysiology, progression, and treatment response. In this review, we detail the use of molecular imaging to delineate host-pathogen interactions, elucidate antimicrobial pharmacokinetics, and monitor treatment response. We also discuss the utility of pathogen-specific radiotracers to accurately diagnose CNS infections and strategies to develop radiotracers that would cross the blood-brain barrier.

Hybrid Polypyrrole and Polydopamine Nanosheets for Precise Raman/Photoacoustic Imaging and Photothermal Therapy

The development of near-infrared light responsive conductive polymers provides a useful theranostic platform for malignant tumors by maximizing spatial resolution with deep tissue penetration for diagnosis and photothermal therapy. Herein, the self-assembly of ultrathin 2D polypyrrole nanosheets utilizing dopamine as a capping agent and a monolayer of octadecylamine as a template is demonstrated. The 2D polypyrrole-polydopamine nanostructure has tunable size distribution which shows strong absorption in the first and second near-infrared windows, enabling photoacoustic imaging and photothermal therapy. The hybrid double-layer is demonstrated to increase Raman intensity for 3D Raman imaging (up to two orders of magnitude enhancement and spatial resolution up to 1 µm). The acidic environment drives reversible doping of polypyrrole, which can be detected by Raman spectroscopy. The combined properties of the nanosheets can substantially enhance performance in dual-mode Raman and photoacoustic guided photothermal therapy, as shown by the 69% light to heat conversion efficiency and higher cytotoxicity against cancer spheroids. These pH-responsive features highlight the potential of 2D conductive polymers for applications in accurate, highly efficient theranostics.

Facile and eco-friendly fabrication of biocompatible hydrogel containing CuS@Ser NPs with mechanical flexibility and photothermal antibacterial activity to promote infected wound healing

Bacterial infections can significantly impede wound healing and pose a serious threat to the patient's life. The excessive use of antibiotics to combat bacterial infections has led to the emergence of multi-drug-resistant bacteria. Therefore, there is a pressing need for alternative approaches, such as photothermal therapy (PTT), to address this issue. In this study, for the first time, CuS NPs with photothermal properties were synthesized using sericin as a biological template, named CuS@Ser NPs. This method is simple, green, and does not produce toxic and harmful by-products. These nanoparticles were incorporated into a mixture (XK) of xanthan gum and konjac glucomannan (KGM) to obtain XK/CuS NPs composite hydrogel, which could overcome the limitations of current wound dressings. The composite hydrogel exhibited excellent mechanical flexibility, photothermal response, and biocompatibility. It also demonstrated potent antibacterial properties against both Gram-positive and negative bacteria via antibacterial experiments and accelerated wound healing in animal models. Additionally, it is proved that the hydrogel promoted tissue regeneration by stimulating collagen deposition, angiogenesis, and reducing inflammation. In summary, the XK/CuS NPs composite hydrogel presents a promising alternative for the clinical management of infected wounds, offering a new approach to promote infected wound healing.

Bacteria-Targeted Combined with Photothermal/NO Nanoparticles for the Treatment and Diagnosis of MRSA Infection In Vivo

Currently, undeveloped diagnosis and delayed treatment of bacteria-infected sites in vivo not only expand the risk of tissue infection but are also a major clinical cause of multiple drug-resistant bacterial infections. Herein, an efficient nanoplatform for near-infrared (NIR)-light-controlled release and bacteria-targeted delivery of nitric oxide (NO) combined with photothermal therapy (PTT) is presented. Using maltotriose-decorated mesoporous polydopamine (MPDA-Mal) and BNN6, a smart antibacterial (B@MPDA-Mal) is developed to combine bacterial targeting, gas-controlled release, and PTT. Utilizing bacteria's unique maltodextrin transport system, B@MPDA-Mal can accurately distinguish bacterial infection from sterile inflammation and target the bacteria-infected sites for efficient drug enrichment. Moreover, NIR-light causes MPDA to generate heat, which not only effectively induces BNN6 to produce NO, but also raises the temperature to harm the bacteria further. NO/photothermal combination therapy effectively eliminates biofilm and drug-resistant bacteria. The myositis model of methicillin-resistant Staphylococcus aureus infection is established and indicates that B@MPDA-Mal can successfully eradicate inflammation and abscesses in mice. Meanwhile, magnetic resonance imaging technology is used to monitor the treatment procedure and healing outcomes. Given the aforementioned advantages, the smart antibacterial nanoplatform B@MPDA-Mal can be used as a potential therapeutic tool in the biomedical field against drug-resistant bacterial infections.

Visual Multifunctional Aggregation-Induced Emission-Based Bacterial Cellulose for Killing of Multidrug-Resistant Bacteria

Multidrug-resistant (MDR) bacteria-related wound infections are a thorny issue. It is urgent to develop new antibacterial wound dressings that can not only prevent wounds from MDR bacteria infection but also promote wound healing. Herein, an aggregation-induced emission (AIE) molecule BITT-composited bacterial cellulose (BC) is presented as wound dressings. BC-BITT composites have good transparency, making it easy to monitor the wound healing process through the composite membrane. The BC-BITT composites retain the advantages of biocompatible BC, and display photodynamic and photothermal synergistic antibacterial effects under irradiation of a 660 nm laser. Furthermore, the BC-BITT composites show excellent wound healing performance in a mouse full-thickness skin wound model infected by MDR bacteria, simultaneously with negligible toxicity. This work paves a way for treating clinically troublesome wound infections.

Activity-Based Photoacoustic Probes for Detection of Disease Biomarkers beyond Oncology

The earliest activity-based photoacoustic (PA) probes were developed as diagnostic agents for cancer. Since this seminal work over a decade ago that specifically targeted matrix metalloproteinase-2, PA instrumentation, dye platforms, and probe designs have advanced considerably, allowing for the detection of an impressive list of cancer types. However, beyond imaging for oncology purposes, the ability to selectively visualize a given disease biomarker, which can range from aberrant enzymatic activity to the overproduction of reactive small molecules, is also being exploited to study a myriad of noncancerous disease states. In this review, we have assembled a collection of recent papers to highlight the design principles that enable activity-based sensing via PA imaging with respect to biomarker identification and strategies to trigger probe activation under specific conditions.

Enzyme-Triggered Transforming of Assembly Peptide-Modified Magnetic Resonance-Tuned Probe for Highly Sensitive Imaging of Bacterial Infection In Vivo

Confirming bacterial infection at an early stage and distinguishing between sterile inflammation and bacterial infection is still highly needed for efficient treatment. Here, in situ highly sensitive magnetic resonance imaging (MRI) bacterial infection in vivo based on a peptide-modified magnetic resonance tuning (MRET) probe (MPD-1) that responds to matrix metallopeptidase 2 (MMP-2) highly expressed in bacteria-infected microenvironments is achieved. MPD-1 is an assembly of magnetic nanoparticle (MNP) bearing with gadolinium ion (Gd3+ ) modified MMP-2-cleavable self-assembled peptide (P1 ) and bacteria-targeting peptide (P), and it shows T2 -weighted signal due to the assemble of MNP and MRET ON phenomenon between MNP assembly and Gd3+ . Once MPD-1 accumulates at the bacterially infected site, P1 included in MPD-1 is cleaved explicitly by MMP-2, which triggers the T2 contrast agent of MPD-1 to disassemble into the monomer of MNP, leading the recovery of T1 -weighted signal. Simultaneously, Gd3+ detaches from MNP, further enhancing the T1 -weighted signal due to MRET OFF. The sensitive MRI of Staphylococcus aureus (low to 104 CFU) at the myositis site and accurate differentiation between sterile inflammation and bacterial infection based on the proposed MPD-1 probe suggests that this novel probe would be a promising candidate for efficiently detecting bacterial infection in vivo.

The sound of blood: photoacoustic imaging in blood analysis

Blood analysis is a ubiquitous and critical aspect of modern medicine. Analyzing blood samples requires invasive techniques, various testing systems, and samples are limited to relatively small volumes. Photoacoustic imaging (PAI) is a novel imaging modality that utilizes non-ionizing energy that shows promise as an alternative to current methods. This paper seeks to review current applications of PAI in blood analysis for clinical use. Furthermore, we discuss obstacles to implementation and future directions to overcome these challenges. Firstly, we discuss three applications to cellular analysis of blood: sickle cell, bacteria, and circulating tumor cell detection. We then discuss applications to the analysis of blood plasma, including glucose detection and anticoagulation quantification. As such, we hope this article will serve as inspiration for PAI's potential application in blood analysis and prompt further studies to ultimately implement PAI into clinical practice.

Value of applying interactive micro-courses on occupational protection in operating room for nursing trainees

This study aimed to investigate the application value of an interactive micro class on occupational protection in the operating room for nursing interns. Using a cluster sampling approach, 200 junior college nursing interns were selected as participants at our hospital, who were practicing from June 2020 to April 2021. They were randomly assigned to either the observation group or the control group, with 100 participants in each. Data on teaching-related evaluation indicators, including clarity of teaching objectives, learning atmosphere, rational use of learning resources, effectiveness of teaching process regulation, and degree of students' participation in activities, were collected for both groups. Additionally, the scores of occupational protection assessment in the operating room, which encompassed physical, chemical, biological, environmental, and physiological and psychological factors, were also recorded. The comparative analysis of teaching-related evaluation indicators between the 2 groups revealed statistically significant differences. Specifically, significant differences were found between the 2 groups in the clarity of teaching objectives (P = .007), learning atmosphere (P < .001), rational use of learning resources (P < .001), effectiveness of teaching process regulation (P = .01), and degree of students' participation in activities (P < .001). Furthermore, the scores of all items in the observation group were higher than those in the control group. Additionally, the comparison results of the scores of the occupational protection assessment in the operating room between the 2 groups showed that while there was no statistically significant difference between the 2 groups before the intervention (P > .05). However, after the intervention, statistically significant differences were found between the 2 groups in physical (P < .001), chemical (P = .001), biological (P < .001), environmental (P < .001), and physiological and psychological factors (P < .001). Additionally, the scores of all items in the observation group were higher than those in the control group. The implementation of the interactive micro class enhanced the quality of teaching related to occupational protection in the operating room for interning nurses, thus verifying its benefits in clinical teaching practices.

Inactive Trojan Bacteria as Safe Drug Delivery Vehicles Crossing the Blood-Brain Barrier

Escherichia coli K1 (EC-K1) can bypass the blood-brain barrier (BBB) and cause meningitis. Excitingly, we find the "dead EC-K1" can safely penetrate the BBB because they retain the intact structure and chemotaxis of the live EC-K1, while losing their pathogenicity. Based on this, we develop a safe "dead EC-K1"-based drug delivery system, in which EC-K1 engulf the maltodextrin (MD)-modified therapeutics through the bacteria-specific MD transporter pathway, followed by the inactivation via UV irradiation. We demonstrate that the dead bacteria could carry therapeutics (e.g., indocyanine green (ICG)) and together bypass the BBB after intravenous injection into the mice, delivering ∼3.0-fold higher doses into the brain than free ICG under the same conditions. What is more, all mice remain healthy even after 14 days of intravenous injection of ∼10⁹ CFU of inactive bacteria. As a proof of concept, we demonstrate the developed strategy enables the therapy of bacterial meningitis and glioblastoma in mice.

Smart One-for-All Agent with Adaptive Functions for Improving Photoacoustic /Fluorescence Imaging-Guided Photodynamic Immunotherapy

Multifunctional phototheranostics that integrate several diagnostic and therapeutic strategies into one platform hold great promise for precision medicine. However, it is really difficult for one molecule to possess multimodality optical imaging and therapy properties that all functions are in the optimized mode because the absorbed photoenergy is fixed. Herein, a smart one-for-all nanoagent that the photophysical energy transformation processes can be facilely tuned by external light stimuli is developed for precise multifunctional image-guided therapy. A dithienylethene-based molecule is designed and synthesized because it has two light-switchable forms. In the ring-closed form, most of the absorbed energy dissipates via nonradiative thermal deactivation for photoacoustic (PA) imaging. In the ring-open form, the molecule possesses obvious aggregation-induced emission features with excellent fluorescence and photodynamic therapy properties. In vivo experiments demonstrate that preoperative PA and fluorescence imaging help to delineate tumors in a high-contrast manner, and intraoperative fluorescence imaging is able to sensitively detect tiny residual tumors. Furthermore, the nanoagent can induce immunogenic cell death to elicit antitumor immunity and significantly suppress solid tumors. This work develops a smart one-for-all agent that the photophysical energy transformation and related phototheranostic properties can be optimized by light-driven structure switch, which is promising for multifunctional biomedical applications.

Tetrazine-Derived Near-Infrared Dye for Targeted Photoacoustic Imaging of Bone

A near-infrared photoacoustic probe was used to image bone in vivo through active and bioorthogonal pretargeting strategies that utilized coupling between a tetrazine-derived cyanine dye and a trans-cyclooctene-modified bisphosphonate. In vitro hydroxyapatite binding of the probe via active and pretargeting strategies showed comparable increases in percent binding vs a nontargeted control. Intrafemoral injection of the bisphosphonate-dye conjugate showed retention out to 24 h post-injection, with a 14-fold increase in signal over background, while the nontargeted dye exhibited negligible binding to bone and signal washout by 4 h post-injection. Intravenous injection, using both active and pretargeting strategies, demonstrated bone accumulation as earlier as 4 h post-injection, where the signal was found to be 3.6- and 1.5-fold higher, respectively, than the signal from the nontargeted dye. The described bone-targeted dye enabled in vivo photoacoustic imaging, while the synthetic strategy provides a convenient building block for developing new targeted photoacoustic probes.

In vivo bioluminescence imaging of natural bacteria within deep tissues via ATP-binding cassette sugar transporter

Most existing bioluminescence imaging methods can only visualize the location of engineered bacteria in vivo, generally precluding the imaging of natural bacteria. Herein, we leverage bacteria-specific ATP-binding cassette sugar transporters to internalize luciferase and luciferin by hitchhiking them on the unique carbon source of bacteria. Typically, the synthesized bioluminescent probes are made of glucose polymer (GP), luciferase, Cy5 and ICG-modified silicon nanoparticles and their substrates are made of GP and D-luciferin-modified silicon nanoparticles. Compared with bacteria with mutations in transporters, which hardly internalize the probes in vitro (i.e., ~2% of uptake rate), various bacteria could robustly engulf the probes with a high uptake rate of around 50%. Notably, the developed strategy enables ex vivo bioluminescence imaging of human vitreous containing ten species of pathogens collected from patients with bacterial endophthalmitis. By using this platform, we further differentiate bacterial and non-bacterial nephritis and colitis in mice, while their chemiluminescent counterparts are unable to distinguish them.

A pH-responsive magnetic resonance tuning probe for precise imaging of bacterial infection in vivo

Accurate and sensitive detection of bacteria is essential for treating bacterial infections. Herein, a pH-responsive magnetic resonance tuning (MRET) probe, whose T₁-weighted signal is activated in the bacteria-infected acid microenvironment, is developed for in situ accurately magnetic resonance imaging (MRI) of bacterial infection in vivo. The MRET probe (MDVG-1) is an assembly of paramagnetic enhancer (gadolinium-modified i-motif DNA₃, abbreviated as Gd-DNA₃-Gd) and the precursor of superparamagnetic quencher (DNA and vancomycin-modified magnetic nanoparticle, abbreviated as MDV). The T₁-weighted signal of Gd-DNA₃-Gd is quenched once the formation of MDVG-1 (MRET ON). Interestingly, the MDVG-1 probe was disassembled into the monomers of Gd-DNA₃-Gd and MDV under the bacteria-infected acid microenvironment, resulting significantly enhanced T₁-weighted signal at the infected site (MRET OFF). The pH-responsive MRET probe-based enhanced MRI signal and bacteria targeting significantly improve the distinction between bacterial infectious tissues and sterile inflamed tissues, which provides a promising approach for accurately detecting bacterial infection in vivo. STATEMENT OF SIGNIFICANCE: : Detecting pathogenic bacteria in vivo based on magnetic resonance imaging (MRI) strategy has been exploring recently. Although various bacterial-targeted MRI probes have been developed to image bacteria in vivo, the MRI signal of these MRI probes is always "on", which inevitably generates nonspecific background MRI signals, affecting the accuracy of MRI to a certain extent. In the current study, based on the magnetic resonance tuning (MRET) phenomenon, we present a pH-responsive MRET probe (MDVG-1) with T₂-weighted imaging to T₁-weighted imaging switchable properties to achieve in situ precise imaging of bacterial infection in vivo.

Antisense Oligonucleotides Selectively Enter Human-Derived Antibiotic-Resistant Bacteria through Bacterial-Specific ATP-Binding Cassette Sugar Transporter

Current vehicles used to deliver antisense oligonucleotides (ASOs) cannot distinguish between bacterial and mammalian cells, greatly hindering the preclinical or clinical treatment of bacterial infections, especially those caused by antibiotic-resistant bacteria. Herein, bacteria-specific ATP-binding cassette (ABC) sugar transporters are leveraged to selectively internalize ASOs by hitchhiking them on α (1-4)-glucosidically linked glucose polymers. Compared with their cell-penetrating peptide counterparts, which are non-specifically engulfed by mammalian and bacterial cells, the presented therapeutics consisting of glucose polymer and antisense peptide nucleic-acid-modified nanoparticles are selectively internalized into the human-derived multidrug-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus, and they display a much higher uptake rate (i.e., 51.6%). The developed strategy allows specific and efficient killing of nearly 100% of the antibiotic-resistant bacteria. Its significant curative efficacy against bacterial keratitis and endophthalmitis is also shown. This strategy will expand the focus of antisense technology to include bacterial cells other than mammalian cells.

Photosensitizers with aggregation-induced far-red/near-infrared emission for versatile visualization and broad-spectrum photodynamic killing of pathogenic microbes

The exploration of photosensitizers with aggregation-induced emission (AIE PSs) for efficient visualization and broad-spectrum photodynamic killing of pathogenic microbes is a significant task. Herein, two far-red/near-infrared AIE-active PSs (TBTPy and TBTCy) were attained to show efficient Type I and Type II ROS generation, benefiting from the efficient ISC processes. The attained AIE PSs, especially TBTPy with bright emission, showed advantages in discriminating G⁺ bacteria over G^- bacteria, and distinguishing dead E. coli from lived one. Both TBTPy and TBTCy have the capacity of broad-spectrum photodynamic killing of pathogenic microbes in vitro with considerable safety for mammalian cells. Antimicrobial mechanism is found to be changing osmotic pressure of cytoplasm in E. coli, causing cell deformation and destruction of S. aureus and C. albicans. In vivo anti-infection experiment demonstrated AIE PSs can accelerate the healing process of the burned wounds on rats infected by methicillin-resistant S. aureus (MRSA) or E. coli, indicating their potential to treat tertiary burns in clinical application. Therefore, the attained AIE PSs hold great promise as antimicrobial candidates in infective therapeutic application.

Family of hNQO1 Activatable Near-Infrared Fluoro-Photoacoustic Probes for Diagnosis of Wound Infection and Ulcerative Colitis

Bacterial infections can easily occur when patients mishandle wounds or eat moldy food. The prompt diagnosis of a bacterial infection could effectively reduce the risk of possible anatomical damage. However, non-invasive early detection of bacterial infections is difficult to achieve due to the lack of favorable tools. Here, we designed two hNQO1 fluorescent probes (RX2 and RX3) to visualize bacterial infection after deep learning on the pathogenesis of bacterial infection. RX2 and RX3 enable early detection of bacterial infection and are verified to be, respectively, suitable for fluorescence imaging (FLI) and photoacoustic imaging (PAI) by comparing the signal-to-background ratio of both probes in a mouse model of myositis caused by Escherichia coli infection. In view of the difference in penetration depth between the two imaging modalities, we further applied RX2 for FLI of E. coli-infected wounds and RX3 for PAI of E. coli-infected inflammatory bowel disease, suggesting the great potential of both probes for early diagnosis of bacterial infections.

Recent Advances in Contrast-Enhanced Photoacoustic Imaging: Overcoming the Physical and Practical Challenges

For decades now, photoacoustic imaging (PAI) has been investigated to realize its potential as a niche biomedical imaging modality. Despite its highly desirable optical contrast and ultrasonic spatiotemporal resolution, PAI is challenged by such physical limitations as a low signal-to-noise ratio (SNR), diminished image contrast due to strong optical attenuation, and a lower-bound on spatial resolution in deep tissue. In addition, contrast-enhanced PAI has faced practical limitations such as insufficient cell-specific targeting due to low delivery efficiency and difficulties in developing clinically translatable agents. Identifying these limitations is essential to the continuing expansion of the field, and substantial advances in developing contrast-enhancing agents, complemented by high-performance image acquisition systems, have synergistically dealt with the challenges of conventional PAI. This review covers the past four years of research on pushing the physical and practical challenges of PAI in terms of SNR/contrast, spatial resolution, targeted delivery, and clinical application. Promising strategies for dealing with each challenge are reviewed in detail, and future research directions for next generation contrast-enhanced PAI are discussed.

Rejuvenating the Activity of Usual Antibiotics on Resistant Gram-Negative Bacteria: Recent Issues and Perspectives

Antibiotic resistance continues to evolve and spread beyond all boundaries, resulting in an increase in morbidity and mortality for non-curable infectious diseases. Due to the failure of conventional antimicrobial therapy and the lack of introduction of a novel class of antibiotics, novel strategies have recently emerged to combat these multidrug-resistant infectious microorganisms. In this review, we highlight the development of effective antibiotic combinations and of antibiotics with non-antibiotic activity-enhancing compounds to address the widespread emergence of antibiotic-resistant strains.

Advances in image-guided drug delivery for antibacterial therapy

The emergence of antibiotic-resistant bacterial strains is seriously endangering the global healthcare system. There is an urgent need for combining imaging with therapies to realize the real-time monitoring of pathological condition and treatment progress. It also provides guidance on exploring new medicines and enhance treatment strategies to overcome the antibiotic resistance of existing conventional antibiotics. In this review, we provide a thorough overview of the most advanced image-guided approaches for bacterial diagnosis (e.g., computed tomography imaging, magnetic resonance imaging, photoacoustic imaging, ultrasound imaging, fluorescence imaging, positron emission tomography, single photon emission computed tomography imaging, and multiple imaging), and therapies (e.g., photothermal therapy, photodynamic therapy, chemodynamic therapy, sonodynamic therapy, immunotherapy, and multiple therapies). This review focuses on how to design and fabricate photo-responsive materials for improved image-guided bacterial theranostics applications. We present a potential application of different image-guided modalities for both bacterial diagnosis and therapies with representative examples. Finally, we highlighted the current challenges and future perspectives image-guided approaches for future clinical translation of nano-theranostics in bacterial infections therapies. We envision that this review will provide for future development in image-guided systems for bacterial theranostics applications.

Recent Progress in Type I Aggregation-Induced Emission Photosensitizers for Photodynamic Therapy

In modern medicine, precision diagnosis and treatment using optical materials, such as fluorescence/photoacoustic imaging-guided photodynamic therapy (PDT), are becoming increasingly popular. Photosensitizers (PSs) are the most important component of PDT. Different from conventional PSs with planar molecular structures, which are susceptible to quenching effects caused by aggregation, the distinct advantages of AIE fluorogens open up new avenues for the development of image-guided PDT with improved treatment accuracy and efficacy in practical applications. It is critical that as much of the energy absorbed by optical materials is dissipated into the pathways required to maximize biomedical applications as possible. Intersystem crossing (ISC) represents a key step during the energy conversion process that determines many fundamental optical properties, such as increasing the efficiency of reactive oxygen species (ROS) production from PSs, thus enhancing PDT efficacy. Although some review articles have summarized the accomplishments of various optical materials in imaging and therapeutics, few of them have focused on how to improve the phototherapeutic applications, especially PDT, by adjusting the ISC process of organic optics materials. In this review, we emphasize the latest advances in the reasonable design of AIE-active PSs with type I photochemical mechanism for anticancer or antibacterial applications based on ISC modulation, as well as discuss the future prospects and challenges of them. In order to maximize the anticancer or antibacterial effects of type I AIE PSs, it is the aim of this review to offer advice for their design with the best energy conversion.

Malto-oligosaccharides as critical functional ingredient: a review of their properties, preparation, and versatile applications

Malto-oligosaccharides (MOS) are α-1,4 glycosidic linked linear oligosaccharides of glucose, which have a diverse range of functional applications in the food, pharmaceutical, and other industries. They can be used to modify the physicochemical properties of foods thereby improving their quality attributes, or they can be included as prebiotics to improve their nutritional attributes. The degree of polymerization of MOS can be controlled by using specific enzymes, which means their functionality can be tuned for specific applications. In this article, we review the chemical structure, physicochemical properties, preparation, and functional applications of MOS in the food, health care, and other industries. Besides, we offer an overview for this saccharide from the perspective of prospect functional ingredient, which we feel lacks in the current literature. MOS could be expected to provide a novel promising substitute for functional oligosaccharides.

Biomedical Photoacoustic Imaging for Molecular Detection and Disease Diagnosis: "Always-On" and "Turn-On" Probes

Photoacoustic (PA) imaging is a nonionizing, noninvasive imaging technique that combines optical and ultrasonic imaging modalities to provide images with excellent contrast, spatial resolution, and penetration depth. Exogenous PA contrast agents are created to increase the sensitivity and specificity of PA imaging and to offer diagnostic information for illnesses. The existing PA contrast agents are categorized into two groups in this review: "always-on" and "turn-on," based on their ability to be triggered by target molecules. The present state of these probes, their merits and limitations, and their future development, is explored.

NIR-II bioimaging of small molecule fluorophores: From basic research to clinical applications

Due to the low autofluorescence and deep-photo penetration, the second near-infrared region fluorescence imaging technology (NIR-II, 1000-2000 nm) has been widely utilized in basic scientific research and preclinical practice throughout the past decade. The most attractive candidates for clinical translation are organic NIR-II fluorophores with a small-molecule framework, owing to their low toxicity, high synthetic repeatability, and simplicity of chemical modification. In order to enhance the translation of small molecule applications in NIR-II bioimaging, NIR-II fluorescence imaging technology has evolved from its usage in cells to the diagnosis of diseases in large animals and even humans. Although several examples of NIR-II fluorescence imaging have been used in preclinical studies, there are still many challenges that need to be addressed before they can finally be used in clinical settings. In this paper, we reviewed the evolution of the chemical structures and photophysical properties of small-molecule fluorophores, with an emphasis on their biomedical applications ranging from small animals to humans. We also explored the potential of small-molecule fluorophores.

Cyclic topology enhances the killing activity of polycations against planktonic and biofilm bacteria

Bacterial biofilms, as a fortress to protect bacteria, enhance resistance to antibiotics because of their limited penetration, which has become a major threat to current anti-infective therapy. Antimicrobial polycations have received wide attention to kill planktonic bacteria because of their unique antimicrobial mechanism without drug resistance but it is still hard to kill the bacteria in the deep of the biofilm. Unlike linear polymers, the cyclic topology has been demonstrated with enhanced penetration in tissues, which is attributed to the lack of end groups, constrained conformation and a smaller hydrodynamic volume, opening a new sight of polycations in the antibacterial application against biofilms. Here, polycations with different topologies including linear and cyclic polycations were synthesized and their killing activity against planktonic and biofilm bacteria was studied. The experimental results showed the enhanced antibacterial activity of cyclic polycations for planktonic bacteria, which is presumably attributed to their smaller hydrodynamic volume, higher local density of positive charge and more interactions between cation units and the bacterial membrane than their linear analogues. Besides, cyclic polycations exhibit enhanced killing effect for biofilm bacteria and inhibition effect for biofilms with 5-7 times and 2-3 times enhancements than the linear polycations, respectively. Furthermore, an Escherichia coli infection model on mice was established and the therapeutic effects of cyclic and linear polycations were evaluated. Compared with the linear polycations, the cyclic polycations exhibited enhanced antibacterial activity with an ∼4 times increase, promoting the healing of the infected wounds. This work provides a new perspective in the development of antimicrobial polycations, which are promising therapeutic agents to kill planktonic and biofilm bacteria without drug resistance.

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.

Exploring BODIPY derivatives as photosensitizers for antibacterial photodynamic therapy

There is urgently needed to develop efficient and safe antimicrobials to replace traditional antibiotics for fighting drug-resistant bacteria. Antimicrobial photodynamic therapy (aPDT), which is a promising antimicrobial strategy that can minimize antibiotic resistance and reduce systemic side effects. Boron-dipyrromethene (BODIPY) is a type of fascinating photosensitizers (PSs) for improving aPDT due to the tunable structures and photophysical features. Herein, six kinds of BODIPY derivatives (BDP1-BDP6) modified with different atoms or groups such as iodine atoms, thiophene, cyano, phenyl, aldehyde and nitro groups were synthesized and their photophysical behaviors were characterized. The results indicated that BDP3, which had 2, 6-diiodo and 8-phenyl substitution, was the best PS candidate with the highest reactive oxygen species (ROS) generation efficacy. BDP3 and BDP5 could rapidly kill Staphylococcus aureus (S. aureus) with the minimum inhibitory concentration (MIC) of 10 nM upon illumination. They also possessed excellent biofilm inhibition ability against S. aureus and could efficaciously restrain the formation of bacterial biofilm. The results of Live/Dead staining assay and scanning electron microscopy (SEM) demonstrated that BDP3 destroyed the cell membrane structure of bacteria by generating ROS, which ultimately led to bacterial lysis and death. Finally, the biosafety evaluation toward the mouse fibroblasts (L929 cells) suggested BDP3 had good cytocompatibility. This work exhibits the great potential of rational designs of PS for aPDT applications.

Persistent Luminescence-Based Theranostics for Real-Time Monitoring and Simultaneously Launching Photodynamic Therapy of Bacterial Infections

External light irradiation is usually required in bacterial infection theranostics; however, it is always accompanied by limited light penetration, imaging interference, and incomplete bacterial destruction. Herein, a feasible "image-launching therapy" strategy is developed to integrate real-time optical imaging and simultaneous photodynamic therapy (PDT) of bacterial infections into persistent luminescence (PL) nanoparticles (NPs). Mesoporous silica NPs are used as a substrate for in situ deposition of PL nanodots of ZnGa₂ O₄ :Cr³⁺ to obtain mPL NPs, followed by surface grafting with silicon phthalocyanine (Si-Pc) and electrostatic assembly of cyanine 7 (Cy7) to fabricate mPL@Pc-Cy NPs. The PL emission of light-activated mPL@Pc-Cy NPs is quenched by Cy7 assembly at physiological conditions through the fluorescence resonance energy transfer effect, but is rapidly restored after disassembly of Cy7 in response to bacterial infections. The self-illuminating capabilities of NPs avoid tissue autofluorescence under external light irradiation and achieve real-time colorimetric imaging of bacterial infections. In addition, the afterglow of mPL NPs can persistently excite Si-Pc photosensitizers to promote PDT efficacy for bacterial elimination and accelerate wound full recovery with normal histologic features. Thus, this study expands the theranostic strategy for precise imaging and simultaneous non-antibiotic treatment of bacterial infections without causing side effects to normal tissues.

Bacteria eat nanoprobes for aggregation-enhanced imaging and killing diverse microorganisms

Currently optical-based techniques for in vivo microbial population imaging are limited by low imaging depth and highly light-scattering tissue; and moreover, are generally effective against only one specific group of bacteria. Here, we introduce an imaging and therapy strategy, in which different bacteria actively eat the glucose polymer (GP)-modified gold nanoparticles through ATP-binding cassette (ABC) transporter pathway, followed by laser irradiation-mediated aggregation in the bacterial cells. As a result, the aggregates display ~15.2-fold enhancement in photoacoustic signals and ~3.0-fold enhancement in antibacterial rate compared with non-aggregated counterparts. Significantly, the developed strategy allows ultrasensitive imaging of bacteria in vivo as low ~10⁵ colony-forming unit (CFU), which is around two orders of magnitude lower than most optical contrast agents. We further demonstrate the developed strategy enables the detection of ~10⁷ CFU bacteria residing within tumour or gut. This technique enables visualization and treatment of diverse bacteria, setting the crucial step forward the study of microbial ecosystem.

The authors demonstrate a strategy for bacterial uptake of gold nanoparticles modified with glucose polymer. The particles aggregate in the bacterial cells upon laser irradiation, resulting in enhanced photoacoustic signal and antibacterial activity, enabling sensitive imaging of bacteria in vivo.

Fluorescent probe strategy for live cell distinction

Live cell discrimination is the first and essential step to understand complex biosystems. Conventional cell discrimination involving various antibodies relies on selective surface biomarkers. Compared to antibodies, the fluorescent probe strategy allows the utilisation of intracellular biomarkers, providing broader options with unique chemical principles to achieve the live cell distinction. In general, fluorescent probes can be retained in cells by interacting with biomolecules, accumulating via transporters, and participating in metabolism. Based on the target difference, fluorescent probe strategy can be divided into several categories: protein-oriented live cell distinction (POLD), carbohydrate-oriented live cell distinction (COLD), DNA-oriented live cell distinction (DOLD), gating-oriented live cell distinction (GOLD), metabolism-oriented live cell distinction (MOLD) and lipid-oriented live cell distinction (LOLD). In this review, we will outline the concepts and mechanisms of different strategies, introduce their applications in cell-type discrimination, and discuss their advantages and challenges in this area. We expect this tutorial will provide a new perspective on the mechanisms of fluorescent probe strategy and facilitate the development of cell-type-specific probes.