Improving the spatial resolution and signal-to-noise ratio of ultrasound switchable fluorescence imaging.

Ultrasound switchable fluorescence (USF) imaging, a hybrid imaging technology that combines the advantages of both fluorescence sensitivity and acoustic resolution in centimeter-deep tissue, has great potential for biomedical different applications. A camera-based USF imaging system reveals its capability of capturing both spatial and temporal dynamics of the USF signal in tissue. In this study, various algorithms were explored to enhance the spatial resolution and signal-to-noise ratio (SNR) of USF images, utilizing temporal and spatial information from a camera-based time-domain USF imaging system. The correlation method proved effective in boosting SNR, while the ascending-slope-weighted method enhanced spatial resolution. Additionally, the spatially back-projection method significantly improved spatial resolution in silicone phantoms. The results underscore the advantages of incorporating temporal and spatial information from USF signals.

A cost-effective approach to measurements of fluorophore temperature sensitivity and temperature change with reasonable accuracy.

The demand for measuring fluorophore temperature sensitivity and temperature change in chemical or biological samples has spurred the search for effective methods. While infrared (IR) light-based thermal devices are popular, they are limited to surface temperature measurement. Fluorescence-based thermometry, which utilizes intensity, lifetime, polarization, and spectrum change, provides the temperature information directly from the samples and can have high temporal and spatial resolution. However, measuring fluorescence can be tricky and expensive. A cost-effective approach to achieving reasonable accuracy is highly desired. This study introduces such an approach, employing a light-emitting diode (LED) for fluorophore excitation and a laser diode (LD) for sample heating, with a phone camera recording fluorescence changes. A data processing method converts the video into digital data, processed through digital filters. Utilizing a small-volume cuvette enhances heating efficiency. This study serves as a practical guide for inexperienced individuals, including students, instructors, and researchers, facilitating entry into the field and navigating the complexities of fluorescence-based thermometry.

Ultrasound-switchable fluorescence thermometry with dual detection channels using temperature-sensitive liposomes.

Temperature measurements in biological tissues play a crucial role in studying metabolic activities. In this study, we introduce a noninvasive thermometry technique based on two-color ultrasound-switchable fluorescence (USF). This innovative method allows for a local temperature mapping within a microtube filled with temperature-sensitive liposomes as nano imaging agents. By measuring the temperature-dependent fluorescence emission of the liposomes using a spectrometer, we identify four characteristic temperatures. The local background temperature can be estimated by analyzing the corresponding appearance time of these four characteristic temperatures in the dynamic USF signals captured by a camera-based USF system with two detection channels. Simultaneous measurements with an infrared (IR) camera showed a 0.38°C ± 0.27°C difference between USF thermometry and IR thermography in a physiological temperature range of 36.48°C-40.14°C. This shows that the two-color USF thermometry technique is a reliable, noninvasive tool with excellent spatial and thermal resolution.

In vivo tumor ultrasound-switchable fluorescence imaging via intravenous injections of size-controlled thermosensitive nanoparticles.

Near-infrared fluorescence imaging has emerged as a noninvasive, inexpensive, and ionizing-radiation-free monitoring tool for assessing tumor growth and treatment efficacy. In particular, ultrasound switchable fluorescence (USF) imaging has been explored with improved imaging sensitivity and spatial resolution in centimeter-deep tissues. This study achieved size control of polymer-based and indocyanine green (ICG) encapsulated USF contrast agents, capable of accumulating at the tumor after intravenous injections. These nanoprobes varied in size from 58 nm to 321 nm. The bioimaging profiles demonstrated that the proposed nanoparticles can efficiently eliminate the background light from normal tissue and show a tumor-specific fluorescence enhancement in the BxPC-3 tumor-bearing mice models possibly via the enhanced permeability and retention effect. In vivo tumor USF imaging further proved that these nanoprobes can effectively be switched 'ON' with enhanced fluorescence in response to a focused ultrasound stimulation in the tumor microenvironment, contributing to the high-resolution USF images. Therefore, our findings suggest that ICG-encapsulated nanoparticles are good candidates for USF imaging of tumors in living animals, indicating their great potential in optical tumor imaging in deep tissue.

Noninvasive measurement of local temperature using ultrasound-switchable fluorescence.

Measuring the local background temperature in diseased and inflamed tissues is highly desirable, especially in a non-invasive way. In this work, ultrasound-switchable fluorescence (USF) technique was utilized to estimate the local background temperature for the first time by analyzing the temperature dependence of fluorescence emission from USF contrast agents induced by a focused ultrasound (FU) beam. First, temperature-sensitive USF agents with distinct temperature switching-on thresholds were synthesized, and their thermal switching characteristics were quantified using an independent spectrometer system. Second, the USF contrast agent suspension was injected into a microtube that was embedded into a phantom and the dynamic USF signal was acquired using a camera-based USF system. The differential profile of the measured dynamic USF signal was computed and compared with the thermal switching characteristics. This allowed for the calculation of the local background temperature of the sample in the FU focal volume based on the estimation of heating speed. An infrared (IR) camera was used to acquire the surface temperature of the sample and further compare it with the USF system. The results showed that the difference between the temperatures acquired from the USF thermometry and the IR thermography was 0.64 ± 0.43 °C when operating at the physiological temperature range from 35.27 to 39.31 °C. These results indicated the potential use of the USF system for measuring the local temperature in diseased tissues non-invasively. The designed USF-based thermometry shows a broad application prospect in high spatial resolution temperature imaging with a tunable measurement range in deep tissue.

Characterization of Collagen Binding Activity of Clostridium perfringens Strains Isolated from Broiler Chickens.

Clostridium perfringens is the etiological agent for necrotic enteritis (NE) in broiler chickens, which causes a substantial economic loss of an estimated USD 6 billion annually in the global poultry industry. Collagen adhesion is involved in the NE pathogenesis in poultry. In this study, the binding capabilities of chicken C. perfringens isolates of various genetic backgrounds (netB-tpeL-, netB+tpeL-, netB+tpeL+) to collagen types I-V and gelatin were examined, and the putative adhesin protein cnaA gene was investigated at the genomic level. In total, 28 C. perfringens strains from healthy and NE-inflicted sick chickens were examined. The results on collagen adhesin-encoding gene cnaA by the quantitative-PCR results indicated that netB-tpeL- isolates had much lower copies of the detectable cnaA gene than netB+ isolates (10 netB+tpeL- isolates, 5 netB+tpeL+ isolates). Most of the virulent C. perfringens isolates demonstrated collagen-binding abilities to types I-II and IV-V, while some strains showed weak or no binding to collagen type III and gelatin. However, the netB+tpeL+ isolates showed significantly higher binding capabilities to collagen III than netB-tpeL- and netB+tpeL- isolates. The data in this study suggest that the collagen-binding capability of clinical C. perfringens isolates correlates well with their NE pathogenicity levels, especially for C. perfringens isolates carrying genes encoding crucial virulence factors and virulence-associated factors such as netB, cnaA, and tpeL. These results indicate that the presence of the cnaA gene may be correlated with C. perfringens virulence (particularly for netB+ isolates).

Size effect of liposomes on centimeter-deep ultrasound-switchable fluorescence imaging and ultrasound-controlled release.

Liposomes have been widely used in both medical imaging and drug delivery fields due to their excellent biocompatibility and easy surface modification. Recently our lab reported for the first-time the implementation of temperature-sensitive and indocyanine green (ICG)-encapsulated liposome microparticles for in vivo ultrasound-switchable fluorescence (USF) imaging. A previous study showed that liposome microparticles achieved USF imaging in centimeter-deep tissue. This study aimed to control the size of liposomes at the nanoscale and study the size effect on the USF imaging depth. Also, we explored the feasibility of combining USF imaging with ultrasound-controlled release. Liposomes were synthesized via the hydration method and the size was controlled by an extruding process. Characterization parameters, including fluorescence profile, spectra, size, stability, encapsulation efficiency, and ultrasound-controlled release, were evaluated. USF imaging in blood serum was conducted successfully in a phantom model, and an imaging depth study was conducted at 1.0 cm and 2.5 cm and confirmed that nano-sized liposomes had a stronger USF signal than micron-sized liposomes. Additionally, releasing tests indicated that both ultrasound power and exposure time affected the release efficiency in that increasing the power and extending the exposure time led to higher release efficiency. Above all, this study shows the potential for using liposomes for USF imaging and ultrasound-controlled release.

Elevated CTSL Gene Expression Correlated with Proinflammatory Cytokines in Omental Adipose Tissue of Patients with Obesity.

Purpose: Cathepsin L (CTSL) and B (CTSB) were lysosomal proteases, and their expression and activity contribute to the progression of inflammation in obese rodents. Our aim was to investigate CTSB and CTSL expression in omental adipose tissue (AT) of patients with obesity and to correlate CTSB and CTSL expression with proinflammatory cytokines (CCL-2, IL-6 and IL-1ß). Patients and Methods: A total of 12 patients without obesity (NOB) and 51 patients with obesity (OB) were involved in this study. Omental AT was collected from all the participants for RNA extraction. Expressions of CTSB, CTSL and proinflammatory cytokines (CCL-2, IL-6 and IL-1ß) were qualified with qRT-PCR. BMI (body mass index) and metabolic parameters were measured. Results: The mRNA expression levels of both CTSB and CTSL were upregulated in the OB group (t = 2.693, P < 0.05; t = 2.849, P<0.01) and were related to TC levels (Std.ß=0.443, P<0.05; Std.ß=0.439, P<0.05). However, only the CTSB level was related to BMI (Std.ß=0.261, P<0.05). In multiple regression analysis, CTSL was independently associated with CCL-2, IL-6 and IL-1ß levels (Std.ß=0.352-0.462, P<0.05). Conclusion: CTSB and CTSL gene expressions were elevated in the omental AT of OB group. CTSL, but not CTSB, was positively correlated with proinflammatory cytokines independently, suggesting that the dysregulation of CTSL may play a significant role in the inflammatory process.

Interstitial fluid streaming in deep tissue induced by ultrasound momentum transfer for accelerating nanoagent transport and controlling its distribution.

Objective.This study aims to theoretically investigate the dynamics of ultrasound-induced interstitial fluid streaming and tissue recovery after ultrasound exposure for potentially accelerating nanoagent transport and controlling its distribution in tissue.Approach.Starting from fundamental equations, the dynamics of ultrasound-induced interstitial fluid streaming and tissue relaxation after an ultrasound exposure were modeled, derived and simulated. Also, both ultrasound-induced mechanical and thermal effects were considered in the models.Main results.The proposed new mechanism was named squeezing interstitial fluid via transfer of ultrasound momentum (SIF-TUM). It means that an ultrasound beam can squeeze the tissue in a small focal volume from all the directions, and generate a macroscopic streaming of interstitial fluid and a compression of tissue solid matrix. After the ultrasound is turned off, the solid matrix will recover and can generate a backflow. Rather than the ultrasound pressure itself or intensity, the streaming velocity is determined by the dot product of the ultrasound pressure gradient and its conjugate. Tissue and nanoagent properties also affect the streaming and recovery velocities.Significance.The mobility of therapeutic or diagnostic agents, such as drugs, drug carriers, or imaging contrast agents, in the interstitial space of many diseased tissues, such as tumors, is usually extremely low because of the inefficiency of the natural transport mechanisms. Therefore, the interstitial space is one of the major barriers hindering agent deliveries. The ability to externally accelerate agent transport and control its distribution is highly desirable. Potentially, SIF-TUM can be a powerful technology to accelerate agent transport in deep tissue and control the distribution if appropriate parameters are selected.

Immunization with Pooled Antigens for Clostridium perfringens Conferred Partial Protection against Experimental Necrotic Enteritis in Broiler Chickens.

Necrotic enteritis (NE) is a multifactorial and important enteric infectious disease etiologically caused by pathogenic C. perfringens infection, accounting for the estimated loss of around USD 6 billion in the global poultry industry. The increasing incidence of NE was found to be associated with the voluntary reduction or withdrawal of antibiotic growth promoters from animal feed during recent years. Therefore, the development of effective vaccines specific to NE assumes a priority for the poultry industry. This study aimed to identify the potential C. perfringens proteins as vaccine targets for NE. Three recombinant C. perfringens proteins targeting five antigens were prepared: two chimeric proteins (alpha-toxin and NetB, fructose-1,6-bisphosphate aldolase (FBA) and a zinc metalloprotease (Zm)), and one single collagen adhesion protein (Cna). Their protection efficacies were evaluated with a potent challenge model of Eimeria maxima/C. perfringens dual infections using a netB+tpeL+ C. perfringens strain. Young chicks were immunized twice subcutaneously with adjuvanted C. perfringens proteins on Days 4 and 15. At six days after the second immunization, the chickens immunized with Cna, FBA, and Zm antigens, and alpha-toxin had much higher serum antibody titers than unvaccinated controls prior to the challenge. Following the challenge, the pooled antigen-immunized group demonstrated no mortality and the least lesion scores against virulent challenge. The results indicate that the immunization with multicomponent antigens, including C. perfringens housekeeping protein Cna, may confer partial protection.

Repeat hepatic resection versus percutaneous ablation for the treatment of recurrent hepatocellular carcinoma: meta-analysis.

BACKGROUND: The efficacy of repeat hepatic resection (rHR) in the treatment of recurrent hepatocellular carcinoma compared with radiofrequency or microwave ablation after resection of the primary tumour remains controversial. A systematic review and meta-analysis were performed to compare the safety and efficacy of these procedures. METHODS: PubMed, Embase, Scopus, Cochrane Library, and China National Knowledge Infrastructure databases were systematically searched to identify related studies published before 10 October 2021. Overall and recurrence-free survival after different treatments were compared based on pooled hazard ratios with a random-effects model. RESULTS: Two randomized clinical trials and 28 observational studies were included, involving 1961 and 2787 patients who underwent rHR and ablation respectively. Median perioperative mortality in both groups was zero but patients in the rHR group had higher median morbidity rates (17.0 per cent) than those in the ablation group (3.3 per cent). rHR achieved significantly longer recurrence-free survival than ablation (HR 0.79, 95 per cent c.i. 0.70 to 0.89, P < 0.001), while both groups had similar overall survival (HR 0.93, 95 per cent c.i. 0.83 to 1.04, P = 0.18). CONCLUSION: rHR and ablation based on radio- or microwaves are associated with similar overall survival in patients with recurrent hepatocellular carcinoma after resection of the primary tumour.

Thermo- and pH-sensitive nanoparticles of poly (N-isopropylacrylamide-decenoic acid-1-vinylimidazole) for ultrasound switchable fluorescence imaging.

We herein report the synthesis of poly (9-decenoic acid-1-vinylimidazole-N-isopropylacrylamide) nanoparticles containing indocyanine green (ICG) in one pot and in water phase throughout the reaction. We have shown that copolymers of 9-decenoic acid and 1-vinylimidazole, or 9-decenoic acid alone, have an enhanced sensitivity to pH values between 7.4 and 6.8 and are superior to the widely used acrylic acid. We have also shown that incorporation of acidic comonomers leads to the favorable outcome of a higher fluorescence signal intensity in lower pH values, whereas the opposite is true of basic comonomers, where the fluorescence signal intensity is lower at low pH values. It was shown that to keep the pH response favorable the molar ratio of basic comonomers to acidic comonomers should roughly equal 1:4. We controlled the lower critical solution temperature (LCST) of the nanoparticles from around 30 to 38°C for different applications by adding acrylamide comonomers. Finally, the nanoparticles at varying pH values, when imaged by an ultrasound switchable fluorescence (USF) imaging system, showed pH sensitivity and thermosensitivity at physiological and tumor pH.

Effect of Thoracic Paravertebral Nerve Block on Blood Coagulation in Patients After Thoracoscopic Lobectomy: A Prospective Randomized Controlled Clinical Trial.

PURPOSE: Ultrasound-guided thoracic paravertebral block (TPVB) has become increasingly popular for postoperative analgesia after thoracic surgery. We designed this prospective, randomized, double-blind, placebo-controlled trial to investigate the effect of TPVB on blood coagulation in patients after thoracoscopic lobectomy. PATIENTS AND METHODS: Sixty patients scheduled for thoracoscopic lobectomy were randomly allocated to two groups. Patients underwent ultrasound-guided TPVB with 0.33% ropivacaine (T group) or 0.9% saline (C group) at the end of the surgery under general anesthesia. Patient-controlled intravenous analgesia (PCIA) was administered for both group after the surgery. The primary outcome was the thromboelastogram (TEG) parameters before anesthesia (T0), at the end of operation (T1) and in 1 day (T2) and 2 days (T3) after the operation, the second outcomes were the analgesic effect and the amount of intraoperative opioid consumption, operation time, infusion volume, blood loss and urine volume. RESULTS: The visual analog scale (VAS) scores in group T were lower than group C (P < 0.05). In group T, compared with T0, the R value at T1 and T2 is significantly reduced, and the K value at T1 were significantly shortened, the α-angle and MA value at T1 were significantly increased (P < 0.05). In group C, compared with T0, the R value and K value were significantly shortened, the α-angle and MA value were significantly increased at all postoperative time points (P < 0.05). Compared with group C at the same time point, the R and K values of group T were significantly longer, and the α-angle and MA values were significantly reduced at T2 and T3 points, with statistically significant differences (P<0.05). CONCLUSION: TPVB is beneficial to improve postoperative hypercoagulability and promote postoperative rehabilitation of patients after thoracoscopic lobectomy.

Lower risk of hepatocellular carcinoma with tenofovir than entecavir treatment in subsets of chronic hepatitis B patients: an updated meta-analysis.

BACKGROUND AND AIM: Previous smaller meta-analyses comparing the incidence of hepatocellular carcinoma (HCC) in chronic hepatitis B (CHB) patients treated with tenofovir disoproxil fumarate (TDF) versus entecavir (ETV) provided controversial results. This updated meta-analysis aimed to reliably identify any difference in the HCC incidence between TDF-treated or ETV-treated CHB patients in general or in specific subgroups. METHODS: PubMed, EMBASE, Web of Science, and Cochrane Library were systematically searched for relevant studies with hazard ratios (HRs) for HCC between TDF-treated and ETV-treated CHB patients. Retrieved dates ranged from January 2009 to October 2021. HRs with or without adjustment were pooled with random-effects model. RESULTS: Twenty-four comparative studies involving 37 771 CHB patients treated with TDF and 72 094 treated with ETV were included. TDF was associated with lower risk of HCC compared with ETV, with pooled unadjusted HR of 0.76 (95% confidence interval [CI]: 0.67-0.86) (24 studies) and adjusted HR of 0.81 (95% CI: 0.72-0.91) (21 studies). In propensity score matching cohorts, the TDF superiority was confirmed for unadjusted HR 0.83 (95% CI: 0.71-0.97) (14 studies) and was close to significance for adjusted HR (0.78, 95% CI: 0.58-1.04) (8 studies). Subgroup analyses showed that TDF was associated with lower HCC risk than ETV treatment in CHB patients who were from Asia (adjusted HR: 0.76, 95% CI: 0.66-0.87; 15 studies) or nucleos(t)ide naïve (adjusted HR:0.74, 95% CI: 0.65-0.84; 18 studies). CONCLUSION: Current evidence from a sizable population suggests that TDF is associated with significantly lower HCC risk compared with ETV treatment in patients who are from Asia and/or nucleos(t)ide naïve.

Clostridium perfringens-Induced Host-Pathogen Transcriptional Changes in the Small Intestine of Broiler Chickens.

Clostridium perfringens is an important opportunistic pathogen that may result in toxin-mediated diseases involving food poisoning/tissue gangrene in humans and various enterotoxaemia in animal species. It is a main etiological agent for necrotic enteritis (NE), the most financially devastating bacterial disease in broiler chickens, especially if raised under antibiotic-free conditions. Importantly, NE is responsible for losses of six billion US dollars annually in the global poultry industry. To investigate the molecular mechanisms of C. perfringens-induced pathogenesis in the gut and its microbiome mRNA levels in C. perfringens-infected and non-infected hosts, we used RNA sequencing technology to perform transcriptional analysis of both host intestine and microbiome using our NE model. The growth rate was significantly impaired in chickens infected by C. perfringens. In total, 13,473 annotated chicken genes were differentially expressed between these two groups, with ninety-six genes showing statistical significance (|absolute fold changes| > 2.0, adjusted p value < 0.05). Genes involved in energy production, MHC Class I antigen, translation, ribosomal structures, and amino acid, nucleotide and carbohydrate metabolism from infected gut tissues were significantly down-regulated. The upregulated genes were mainly engaged in innate and adaptive immunity, cellular processes, genetic information processing, and organismal systems. Additionally, the transcriptional levels of four crucial foodborne pathogens were significantly elevated in a synergic relationship with pathogenic C. perfringens infection. This study presents the profiling data that would likely be a relevant reference for NE pathogenesis and may provide new insights into the mechanism of host-pathogen interaction in C. perfringens-induced NE infection in broiler chickens.

Neuroprotection of N-benzyl Eicosapentaenamide in Neonatal Mice Following Hypoxic-Ischemic Brain Injury.

Maca (Lepidium meyenii) has emerged as a popular functional plant food because of its medicinal properties and nutritional value. Macamides, as the exclusively active ingredients found in maca, are a unique series of non-polar, long-chain fatty acid N-benzylamides with multiple bioactivities such as antifatigue characteristics and improving reproductive health. In this study, a new kind of macamide, N-benzyl eicosapentaenamide (NB-EPA), was identified from maca. We further explore its potential neuroprotective role in hypoxic-ischemic brain injury. Our findings indicated that treatment with biosynthesized NB-EPA significantly alleviates the size of cerebral infarction and improves neurobehavioral disorders after hypoxic-ischemic brain damage in neonatal mice. NB-EPA inhibited the apoptosis of neuronal cells after ischemic challenge. NB-EPA improved neuronal cell survival and proliferation through the activation of phosphorylated AKT signaling. Of note, the protective property of NB-EPA against ischemic neuronal damage was dependent on suppression of the p53-PUMA pathway. Taken together, these findings suggest that NB-EPA may represent a new neuroprotectant for newborns with hypoxic-ischemic encephalopathy.

Calcium Channel Protein ORAI1 Mediates TGF-ß Induced Epithelial-to-Mesenchymal Transition in Colorectal Cancer Cells.

Accumulating evidence suggested that calcium release-activated calcium modulator 1(ORAI1), a key calcium channel pore-forming protein-mediated store-operated Ca2+ entry (SOCE), is associated with human cancer. However, its role in colorectal cancer (CRC) progression has not been well studied. Epithelial-mesenchymal transition (EMT) is a multistep process that occurs during the progression of cancers and is necessary for metastasis of epithelial cancer. Transforming growth factor-ß (TGF-ß) is a pleiotropic cytokine that has been shown to induce EMT. In this study, we are aimed at exploring the effects of ORAI1 on TGF-ß1-induced EMT process in CRC cells. Herein, we confirmed ORAI1 expression was higher in CRC tissues than in adjacent non-cancerous tissues by using immunohistochemical staining and Western blot analysis. Higher ORAI1 expression was associated with more advanced clinical stage, higher incidence of metastasis and shorter overall survival. We compared ORAI1 expression in SW480 and SW620 cells, two CRC cell lines with the same genetic background, but different metastatic potential. We found ORAI1 expression was significantly higher in SW620 cells which exhibited higher EMT characteristics. Furthermore, knockdown of ORAI1 suppressed the EMT of SW620 Cells. After induced the EMT process in SW480 cells with TGF-ß1, we found treatment of TGF-ß1 showed a significant increase in cell migration along with the loss of E-cadherin and an increase in N-cadherin and Vimentin protein levels. Also, TGF-ß1 treatment increased ORAI1 expression and was closely associated with the increase of SOCE. Silencing ORAI1 significantly suppressed Ca2+ entry, reversed the changes of EMT-relevant marks expression induced by TGF-ß1, and inhibited TGF-ß1-mediated calpain activation and cell migration. Finally, we blocked SOCE with 2-APB (2-Aminoethyl diphenylborinate), a pharmacological inhibitor. Interestingly, 2-APB and sh-ORAI1 both exhibited similar inhibition effects to the SW480 cells. In conclusion, our results demonstrated that ORAI1 could mediate TGF-ß-Induced EMT by promoting Ca2+ entry and calpain activity in Colorectal Cancer Cells.

Improving sensitivity and imaging depth of ultrasound-switchable fluorescence via an EMCCD-gain-controlled system and a liposome-based contrast agent.

BACKGROUND: The ultrasound-switchable fluorescence (USF) technique was recently developed to achieve high-resolution fluorescence imaging in centimeters-deep tissue. This study introduced strategies to significantly improve imaging sensitivity and depth using an electron multiplying charge-coupled device (EMCCD) camera-based USF imaging system and a newly developed USF contrast agent of indocyanine green (ICG)-encapsulated liposomes. For a quantitative study, a phantom of a sub-millimeter silicone tube embedded in centimeter-thick chicken breast tissue was adopted in this study as a model. METHODS: The synthesized ICG-liposome was characterized and compared with the previously reported ICG-nanogel. The exposure of the EMCCD camera was controlled via the MATLAB (The MathWorks, Inc. USA), instead of an external hardware trigger. The stability of the electron multiplying (EM) gain of the EMCCD camera was compared between two trigger modes: the MATLAB trigger mode and the external hardware trigger mode. The signal-to-noise ratio (SNR) of the USF imaging with different EM gain in various thick tissue was studied. RESULTS: The hydrodynamic size of the ICG-liposome was ~181 nm. The ICG-liposome had a sharper temperature switching curve and a better USF performance than the previously reported ICG-nanogel. The EM gain was more stable in MATLAB trigger mode than the external hardware trigger mode. Although, as usual, the SNR decreased quickly with the increase of the tissue thickness, the proposed strategies improved the SNR and the imaging depth significantly by adopting the novel contrast agent and controlling the EM gain. CONCLUSIONS: We successfully imaged the sub-millimeter silicone tube with an inner diameter of 0.76 mm and an outer diameter of 1.65 mm in 5.5 cm-thick chicken breast tissue using 808 nm excitation light with a low intensity of 28.35 mW/cm2, the improved EMCCD camera-based USF imaging system and the novel ICG-liposomes.

Near-infrared temperature-switchable fluorescence nanoparticles.

BACKGROUND: Near infrared (NIR) environment-sensitive fluorophores are highly desired for many biomedical applications because of its non-invasive operation, high sensitivity and specificity, non-ionizing radiation and deep penetration in biological tissue. When the fluorophores are appropriately encapsulated in or conjugated with some thermal-sensitive polymers, they could work as excellent temperature-sensing probes. METHODS: In this study, we synthesized and characterized a series of NIR temperature-switchable nanoparticles based on two series of NIR fluorophores aza-BODIPY (ADP is used for abbreviation in this work) and Zinc phthalocyanine (ZnPc) and four pluronic polymers (F127, F98, F68 and F38). Encapsulating the fluorophores in the polymers by sonication, we synthesized the nanoparticles that showed switch-like functions of the fluorescence intensity (and/or lifetime) as the temperature, with high switch on-to-off ratio. We also investigated various factors that might change the temperature thresholds (Tth) of the switch functions, in order to control Tth during synthesis. RESULTS: These nanoparticles showed excellent temperature-switchable properties of fluorescence intensity and/or lifetime. Meanwhile, some factors (i.e., pluronic categories and nanoparticles' concentration) significantly affected the nanoparticles' Tths while other (i.e., fluorophore categories) that weakly affected Tths. CONCLUSIONS: By selecting appropriate pluronic categories and adjusting the nanoparticle's concentration, we can synthesize the nanoparticles with a wide range of Tths. These temperature-switchable fluorescence nanoparticles can be used for biomedical imaging and in vivo tissue temperature sensing/imaging.