Percutaneous endoscopic transforaminal discectomy and unilateral biportal endoscopic discectomy for lumbar disc herniation: a comparative analysis of learning curves.

OBJECTIVE: The purpose of this study was to investigate the learning curve of percutaneous endoscopic transforaminal discectomy (PETD) and interlaminar unilateral biportal endoscopic discectomy (UBED) in the treatment of lumbar disc herniation (LDH). METHODS: Between 2018 and 2023, 120 consecutive patients with lumbar disc herniation (LDH) treated by endoscopic lumbar discectomy were retrospectively included. The PETD group comprised 87 cases, and the UBED group comprised 33 cases. Cumulative sum analysis was used to evaluate the learning curve, with the occurrence of complications or unresolved symptoms defined as surgical failure, and variables of different phases of the learning curve being compared. RESULTS: The learning curve analysis identified the cutoff point at 40 cases in the PETD group and 15 cases in the UBED group. In the mastery phase, both PETD and UBED demonstrated a significant reduction in operation times (approximately 38 min for PTED and 49 min for UBED). In both PETD and UBED groups, the surgical failure rates during the learning and mastery phases showed no statistically significant differences. The visual analogue scale at the last follow-up was significantly lower than before surgery in both the PETD and UBED groups. CONCLUSION: PETD and UBED surgery are effective in the treatment of LDH with a low incidence of complications. However, achieving mastery in PETD necessitates a learning curve of 40 cases, while UBED requires a minimum of 15 cases to reach proficiency.

Potential clinical value of fibrinogen-like protein 1 as a serum biomarker for the identification of diabetic cardiomyopathy.

Diabetic individuals with diabetic cardiomyopathy (DbCM) present with abnormal myocardial structure and function. DbCM cannot be accurately diagnosed due to the lack of suitable diagnostic biomarkers. In this study, 171 eligible participants were divided into a healthy control (HC), type 2 diabetes mellitus (T2DM) patients without DbCM (T2DM), or DbCM group. Serum fibrinogen-like protein 1 (FGL-1) and other biochemical parameters were determined for all participants. Serum FGL-1 levels were significantly higher in patients with DbCM compared with those in the T2DM group and HCs. Serum FGL-1 levels were negatively correlated with left ventricular fractional shortening and left ventricular ejection fraction (LVEF) and positively correlated with left ventricular mass index in patients with DbCM after adjusting for age, sex and body mass index. Interaction of serum FGL-1 and triglyceride levels on LVEF was noted in patients with DbCM. A composite marker including serum FGL-1 and triglycerides could differentiate patients with DbCM from those with T2DM and HCs with an area under the curve of 0.773 and 0.789, respectively. Composite marker levels were negatively correlated with N-terminal B-type natriuretic peptide levels in patients with DbCM. Circulating FGL-1 may therefore be a valuable index reflecting cardiac functions in DbCM and to diagnose DbCM.

Impact of perinatal factors on meconium aspiration syndrome in full-term newborns and the construction of a column chart prediction model: An observational study.

To explore the influence of perinatal-related factors on meconium aspiration syndrome (MAS) in full-term neonates and construct a nomogram prediction model for risk stratification of neonatal MAS and adoption of preventive measures. A total of 424 newborns and their mothers who were regularly examined at our hospital between January 2020 and December 2023 who had meconium-contaminated amniotic fluid during delivery were retrospectively selected as participants. Neonates were divided into MAS and non-MAS groups based on whether MAS occurred within 3 days after birth. Data from the 2 groups were analyzed, and factors influencing MAS were screened using multivariate logistic regression analysis. The R3.4.3 software was used to construct a nomogram prediction model for neonatal MAS risk. Receiver operating characteristic (ROC) curve analysis and the Hosmer-Lemeshow goodness-of-fit test were used to evaluate the performance of the model, and its clinical effectiveness was evaluated using a decision curve. Among the 424 neonates with meconium-stained amniotic fluid, 51 developed MAS within 3 days of birth (12.03%). Multivariate logistic regression analysis showed that a low amniotic fluid index before delivery (OR = 2.862, P = .019), advanced gestational age (OR = 0.526, P = .034), cesarean section (OR = 2.650, P = .013), severe amniotic fluid contamination (OR = 4.199, P = .002), low umbilical cord blood pH (OR = 2.938, P = .011), and low neonatal Apgar 1-min score (OR = 3.133, P = .006) were influencing factors of MAS in full-term neonates. Based on the above indicators, a nomogram prediction model for MAS risk of full-term newborns was constructed. The area under the ROC curve of the model was 0.931. The model was also tested for goodness-of-fit deviation (χ2 = 3.465, P = .903). Decision curve analysis found that the model was clinically effective in predicting the net benefit of MAS risk in neonates with meconium-stained amniotic fluid. The construction of a column chart prediction model for neonatal MAS risk based on prenatal amniotic fluid index, gestational age, delivery method, amniotic fluid contamination level, newborn umbilical blood pH value, and Apgar 1-min score has a certain application value.

Solvent-modulated luminescence of carbon dots for ion sensing and fingerprint detection.

Since carbon dots (CDs) with good water solubility are preferred by researchers and biological applications, a hydrothermal method was used to synthesize green fluorescent CDs with an excitation-independent peak at 526 nm using deionized water as the solvent and neutral red as the carbon source. To achieve spectral modulation, the pH of the solvent was adjusted with KOH to obtain orange CDs (O-CDs) in an alkaline environment, with the emission peak red-shifted to 630 nm. The water-soluble CDs were prepared for multidimension sensing as Fe3+ sensing (on/off). Carbon dots dispersed into a silica gel matrix can be used for fingerprint detection of various materials.

Tunable and highly sensitive fluorescent thermometers from La2CaZrO6:Cr3+ with a time-resolved technology.

Non-contact optical temperature measurement can effectively avoid the disadvantages of traditional contact thermometry and thus, become a hot research topic. Herein, a fluorescence intensity ratio (FIR) thermometry using a time-resolved technique based on La2CaZrO6:Cr3+ (LCZO) is proposed, with a maximum relative sensitivity (Sr - FIR) of 2.56% K-1 at 473 K and a minimum temperature resolution of 0.099 K. Moreover, the relative sensitivity and temperature resolution can be effectively controlled by adjusting the width of the time gate based on the time-resolved technique. Our work provides, to our knowledge, new viewpoints into the development of novel optical thermometers with adjustable relative sensitivity and temperature resolution on an as-needed basis.

Virtual reality-based cognitive-behavioural therapy for the treatment of anxiety in patients with acute myocardial infarction: a randomised clinical trial.

Background: The presence of mental health conditions is pervasive in patients who experienced acute myocardial infarction (AMI), significantly disrupting their recovery. Providing timely and easily accessible psychological interventions using virtual reality-based cognitive-behavioural therapy (VR-CBT) could potentially improve both acute and long-term symptoms affecting their mental health. Aims: We aim to examine the effectiveness of VR-CBT on anxiety symptoms in patients with AMI who were admitted to the intensive care unit (ICU) during the acute stage of their illness. Methods: In this single-blind randomised clinical trial, participants with anxiety symptoms who were admitted to the ICU due to AMI were continuously recruited from December 2022 to February 2023. Patients who were Han Chinese aged 18-75 years were randomly assigned (1:1) via block randomisation to either the VR-CBT group to receive VR-CBT in addition to standard mental health support, or the control group to receive standard mental health support only. VR-CBT consisted of four modules and was delivered at the bedside over a 1-week period. Assessments were done at baseline, immediately after treatment and at 3-month follow-up. The intention-to-treat analysis began in June 2023. The primary outcome measure was the changes in anxiety symptoms as assessed by the Hamilton Anxiety Rating Scale (HAM-A). Results: Among 148 randomised participants, 70 were assigned to the VR-CBT group and 78 to the control group. The 1-week VR-CBT intervention plus standard mental health support significantly reduced the anxiety symptoms compared with standard mental health support alone in terms of HAM-A scores at both post intervention (Cohen's d=-1.27 (95% confidence interval (CI): -1.64 to -0.90, p<0.001) and 3-month follow-up (Cohen's d=-0.37 (95% CI: -0.72 to -0.01, p=0.024). Of the 70 participants who received VR-CBT, 62 (88.6%) completed the entire intervention. Cybersickness was the main reported adverse event (n=5). Conclusions: Our results indicate that VR-CBT can significantly reduce post-AMI anxiety at the acute stage of the illness; the improvement was maintained at the 3-month follow-up. Trial registration number: The trial was registered at www.chictr.org.cn with the identifier: ChiCTR2200066435.

Influence of the Original Concrete Strength and Initial Moisture Condition on the Properties Improvement of Recycled Coarse Aggregate via Accelerated Carbonation Reactions.

The physical and mechanical properties of recycled coarse aggregate (RCA) are worse than those of natural coarse aggregate (NCA), and the overall performance of recycled concrete prepared from RCA is worse than that of natural aggregate concrete. Treatment of RCA by CO2-accelerated carbonation effectively improves the macroscopic properties of RCA. The degree of influence of raw material factors, i.e., the original concrete strength (OCS) and initial moisture content (IMC) of RCA, on the carbonation of RCAs is very complex. Herein, an accelerated carbonation experiment for RCA with different material factors as variables was carried out to explore the influence of the abovementioned factors on the physical properties of carbonated recycled coarse aggregate (CRCA). By analyzing the microstructure of the RCA with the best modification effect before and after carbonation, the carbonation modification mechanism of the RCA was revealed. The physical performance indexes, including the apparent density, water absorption and carbonation rate, of the dried RCA with an OCS of C40 and C50 were significantly improved. The research results can provide basic data and theoretical support for promoting the popularization and application of RCA and recycled concrete in practical engineering.

Risk Factors of Serious Adverse Events for Geriatric Hip Fractures: Is it the Frailty or the Timing?

Objective: Preoperative frailty and surgical waiting times are associated with the occurrence of adverse outcomes in patients with hip fractures. Specifically, we aimed to investigate the influence of frailty status and surgical timing on the risk of serious adverse events during hospitalization. Methods: This study utilized an observational single cohort design and included patients aged ≥60 years with a primary diagnosis of hip fracture. Frailty was assessed using the chart-derived frailty index (CFI), which was calculated based on demographic and routine laboratory variables. The primary outcome of interest was the occurrence of in-hospital serious adverse events. A multivariate logistic regression model was utilized to examine the risk factors influencing outcomes. Results: The study included 427 participants, with a mean age of 80.28 ± 8.13 years and 64.2% of whom were female. Patients with high CFI have more comorbidities (P < .001), lower surgical rates (P = .002), and delayed surgical times (P = .033). A total of 239 patients (56.0%) experienced serious adverse events. The high CFI group had a significantly higher occurrence of serious adverse events compared to the low CFI group (73.4% vs 48.5%, P < .001). After adjusting for surgical timing and covariates, the multivariate logistic regression analysis revealed that high frailty significantly increased the risk for serious adverse events (OR = 2.47, 95% CI 1.398-4.412), infection (OR = 1.99, 95% CI 1.146-3.446), acute heart failure (OR = 3.37, 95% CI 1.607-7.045). However, the timing of surgery did not demonstrate any association with these outcomes. In addition, after adjusting for surgical factors, high CFI remains an independent risk factor for these complications. Conclusions: Frailty serves as a reliable predictor of the probability of encountering severe adverse events while hospitalized for elderly individuals with hip fractures. This method has the potential to pinpoint particular modifiable factors that necessitate intervention, whereas the impact of surgical timing remains uncertain and necessitates additional research.

Comparative transcriptomic evidence of physiological changes and potential relationships in vertebrates under different dormancy states.

Dormancy represents a fascinating adaptive strategy for organisms to survive in unforgiving environments. After a period of dormancy, organisms often exhibit exceptional resilience. This period is typically divided into hibernation and aestivation based on seasonal patterns. However, the mechanisms by which organisms adapt to their environments during dormancy, as well as the potential relationships between different states of dormancy, deserve further exploration. Here, we selected Perccottus glenii and Protopterus annectens as the primary subjects to study hibernation and aestivation, respectively. Based on histological and transcriptomic analysis of multiple organs, we discovered that dormancy involved a coordinated functional response across organs. Enrichment analyses revealed noteworthy disparities between the two dormant species in their responses to extreme temperatures. Notably, similarities in gene expression patterns pertaining to energy metabolism, neural activity, and biosynthesis were noted during hibernation, suggesting a potential correlation between hibernation and aestivation. To further explore the relationship between these two phenomena, we analyzed other dormancy-capable species using data from publicly available databases. This comparative analysis revealed that most orthologous genes involved in metabolism, cell proliferation, and neural function exhibited consistent expression patterns during dormancy, indicating that the observed similarity between hibernation and aestivation may be attributable to convergent evolution. In conclusion, this study enhances our comprehension of the dormancy phenomenon and offers new insights into the molecular mechanisms underpinning vertebrate dormancy.

Bibliometric and visualized analysis of hydrogels in organoids research.

Over the past decades, there has been ongoing effort to develop complex biomimetic tissue engineering strategies for in vitro cultivation and maintenance of organoids. The defined hydrogels can create organoid models for various organs by changing their properties and various active molecules. An increasing number of researches has been done on the application of hydrogels in organoids, and a large number of articles have been published on the topic. Although there have been existing reviews describing the application of hydrogels in the field of organoids, there is still a lack of comprehensive studies summarizing and analyzing the overall research trends in this field. The citation can be used as an indicator of the scientific influence of an article in its field. This study aims to evaluate the application of hydrogels in organoids through bibliometric analysis, and to predict the hotspots and developing trends in this field.

[Role and mechanism of gut microbiota and its metabolites in host defense against infection].

The interaction of gut microbiota and its metabolites with the host not only plays an important role in maintaining gut homeostasis and host health, but also is a key link in responding to pathogen infections. A thorough understanding of the changes in gut microbiota and its metabolites during infection, as well as their role and mechanism in host defense against infection, is helpful to guide anti-infection treatment. This review focuses on the role of gut microbiota and their metabolites in host defense against bacterial, fungal, and viral infections, and reveals that they can exert anti-infection effects through resistance mechanisms (inducing antimicrobial substances, training immunity, inhibiting pathogen respiration, directly neutralizing pathogens, immune regulation) and tolerance mechanisms (altering energy metabolism patterns of microbiota, cell proliferation and tissue damage repair, maintaining physiological signal transduction in extraintestinal organs, inflammation regulation, maintaining the integrity of the intestinal barrier), and also summarizes measures to regulate gut microbiota against pathogen infections, in order to provide more ideas for novel anti-infection prevention and treatment strategies targeting gut microbiota and its metabolites.

Adjustable ultraviolet and white light dual emission phosphor Y2Sr(Ga1-yAly)4SiO12:xPr3+ for health lighting.

Mid-ultraviolet light (290-320 nm) can promote human vitamin D synthesis, which helps in the prevention and treatment of rickets and cartilage disease. For people who lack sufficient ultraviolet radiation all year round, it is significant to supplement the ultraviolet component in daily lighting sources. However, there are few luminous materials showing a combination of mid-ultraviolet light and white light emission on the market. Here, we designed a new material, Y2Sr(Ga1-yAly)4SiO12:xPr3+ (YSGAS:xPr3+), which achieves dual emission of 320 nm ultraviolet and white light from a single substrate with a single doped phosphor. Without Al3+ ions, the emission intensity of the Y2SrGa4SiO12:xPr3+ phosphor shows a contribution-dependent relationship, and concentration quenching due to exchange interaction. The crystal field environment was regulated by partially replacing Ga3+ ions with Al3+ ions. After introducing Al3+, YSGAS:xPr3+ phosphors exhibit dual ultraviolet emission (320 nm) and visible light emission. The emission color of YSGAS:xPr3+ can be adjusted by changing the Al3+ concentration, and Y2Sr(Ga0.6Al0.4)4SiO12:1%Pr3+ emits both ultraviolet light and white light. The LED device prepared by using the YSGAS:Pr3+ phosphor and chips shows a color temperature of 4858 K and appropriate CIE coordinates of (0.3474, 0.3390), indicating wide application prospects in the field of "health lighting" for particular populations.

Sulphated Fucooligosaccharide from Sargassum Horneri: Structural Analysis and Anti-Alzheimer Activity.

In the present study, sulfated polysaccharides were obtained by digestion of Sargassum horneri and preparation with enzyme-assisted extraction using three food-grade enzymes, and their anti- Alzheimer's activities were investigated. The results demonstrated that the crude sulfated polysaccharides extracted using AMGSP, CSP and VSP dose-dependently (25-100 µg·mL- 1) raised the spontaneous alternating manner (%) in the Y maze experiment of mice and reduced the escape latency time in Morris maze test. AMGSP, CSP and VSP also exhibited good anti-AChE and moderate anti-BuChE activities. CSP displayed the best inhibitory efficacy against AChE. with IC50 values of 9.77 µM. And, CSP also exhibited good inhibitory selectivity of AChE over BuChE. Next, CSP of the best active crude extract was separated by the preparation type high performance liquid phase to obtain the sulphated fucooligosaccharide section: SFcup (→3-α-L-fucp(2-SO3-)-1→4-α-L-fucp(2,3-SO3-)-1→section), SFcup showed a best inhibitory efficacy against AChE with IC50 values of 4.03 µM. The kinetic research showed that SFcup inhibited AChE through dual binding sites. Moreover, the molecular docking of SFcup at the AChE active site was in accordance with the acquired pharmacological results.

Deep convolutional network-based chest radiographs screening model for pneumoconiosis.

Background: Pneumoconiosis is the most important occupational disease all over the world, with high prevalence and mortality. At present, the monitoring of workers exposed to dust and the diagnosis of pneumoconiosis rely on manual interpretation of chest radiographs, which is subjective and low efficiency. With the development of artificial intelligence technology, a more objective and efficient computer aided system for pneumoconiosis diagnosis can be realized. Therefore, the present study reported a novel deep learning (DL) artificial intelligence (AI) system for detecting pneumoconiosis in digital frontal chest radiographs, based on which we aimed to provide references for radiologists. Methods: We annotated 49,872 chest radiographs from patients with pneumoconiosis and workers exposed to dust using a self-developed tool. Next, we used the labeled images to train a convolutional neural network (CNN) algorithm developed for pneumoconiosis screening. Finally, the performance of the trained pneumoconiosis screening model was validated using a validation set containing 495 chest radiographs. Results: Approximately, 51% (25,435/49,872) of the chest radiographs were labeled as normal. Pneumoconiosis was detected in 49% (24,437/49,872) of the labeled radiographs, among which category-1, category-2, and category-3 pneumoconiosis accounted for 53.1% (12,967/24,437), 20.4% (4,987/24,437), and 26.5% (6,483/24,437) of the patients, respectively. The CNN DL algorithm was trained using these data. The validation set of 495 digital radiography chest radiographs included 261 cases of pneumoconiosis and 234 cases of non-pneumoconiosis. As a result, the accuracy of the AI system for pneumoconiosis identification was 95%, the area under the curve was 94.7%, and the sensitivity was 100%. Conclusion: DL algorithm based on CNN helped screen pneumoconiosis in the chest radiographs with high performance; thus, it could be suitable for diagnosing pneumoconiosis automatically and improve the efficiency of radiologists.

Establishment of nonobstructive coronary microcirculatory disorders in rabbits using three established methods and a comparative study.

To compare the merits and drawbacks of three approaches for establishing a rabbit model of nonobstructive coronary microcirculatory disease, namely, open thoracic subtotal ligation of coronary arteries, ultrasound-guided cardiac microsphere injection, and sodium laurate injection. New Zealand rabbits were allocated to four groups: a normal group (Blank group), an Open-chest group (Open-chest), a microsphere group (Echo-M), and a sodium laurate group (Echo-SL), each comprising 10 rabbits. The rabbits were sacrificed 24 h after the procedures, and their echocardiography, stress myocardial contrast echocardiography, pathology, and surgical times were compared. The results demonstrated varying degrees of reduced cardiac function in all three experimental groups, the Open-chest group exhibiting the most significant decline. The myocardial filling in the affected areas was visually analyzed by myocardial contrast echocardiography, revealing sparse filling at rest but more after stress. Quantitative analysis of perfusion parameters (ß, A, MBF) in the affected myocardium showed reduced values, the Open-chest group having the most severe reductions. No differences were observed in stress myocardial acoustic imaging parameters between the Echo-M and Echo-SL groups. Among the pathological presentations, the Open-chest model predominantly exhibited localized ischemia, while the Echo-M model was characterized by mechanical physical embolism, and the Echo-SL model displayed in situ thrombosis as the primary pathological feature. Inflammatory responses and collagen deposition were observed in all groups, with the severity ranking of Open-chest > Echo-SL > Echo-M. The ultrasound-guided intracardiac injection method used in this experiment outperformed open-chest surgery in terms of procedural efficiency, invasiveness, and maneuverability. This study not only optimizes established cardiac injection techniques but also offers valuable evidence to support clinical investigations through a comparison of various modeling methods.

The relationship between postpartum negative life events and postpartum depression: a moderated mediation model of neuroticism and psychological flexibility.

BACKGROUND: Postpartum depression (PPD) is a major public health problem worldwide. Previous studies have shown that postpartum negative life events and neuroticism are both important risk factors for PPD. However, few studies have considered the role of protective factors in the influence of postpartum negative life events and neuroticism on PPD. Based on the diathesis-stress model and Acceptance and Commitment Therapy (ACT), a moderated mediating model was established to examine the mediating role of neuroticism between postpartum negative life events and PPD, as well as the moderating role of psychological flexibility in this mediating effect. METHODS: A sample of 776 parturients from three different Grade A hospitals in China were assessed using the Edinburgh Postpartum Depression Scale, the Postpartum Negative Life Events Scale, the Neuroticism Subscale of the Big Five Personality Scale, and the Acceptance and Action Questionnaire- II. RESULTS: PPD, postpartum negative life events, neuroticism, and experiential avoidance were significantly positively correlated with one another. Neuroticism partially mediated the relationship between postpartum negative life events and PPD. In this mediation model, the direct path and the second half of the mediation path were moderated by psychological flexibility. Specifically, the links between postpartum negative life events and PPD, as well as between neuroticism and PPD, were stronger when psychological flexibility was low, but weaker when psychological flexibility was high. CONCLUSIONS: The results show that psychological flexibility plays an important role in buffering the negative effects of postpartum negative life events and neuroticism on PPD. These findings provide implications for the prevention and intervention of PPD using an ACT approach.

An improved prediction model for COD measurements using UV-Vis spectroscopy.

In the 21st century, although water quality has been improved in the last two decades, water pollution by organic contaminants has remained a non-negligible issue in China, so Chemical-Oxygen Demand (abbreviated as COD, unit: mg L-1) is often used as the main index to measure the degree of surface water pollution. UV-Vis spectroscopy, as a sensitive and rapid analytical technique, is a green detection technology suitable for automatic online COD detection equipment. However, due to the complex composition of surface water, the interference degree of the UV-Vis spectrum caused by turbidity is strongly correlated with the size, type and color of particulate matter in the solution, which results in noise sensitivity and poor generalization of the current detection model. Therefore, the main purpose of this research is to improve the traditional detection model performance by using deep learning and a spectrum preprocessing algorithm. Firstly, we used an improved noise filter based on discrete wavelet transforms to solve the noise sensitivity. Secondly, we proposed a novel COD detection network to address poor generalization. Thirdly, we collected a total of 2259 water samples' UV-Vis absorption spectra and corresponding COD as a dataset. Then, we pipelined the improved noise removal algorithm and proposed COD detection network, as a complete COD prediction model. Finally, the experiment on the dataset shows that the COD prediction model has a good performance in terms of both noise tolerance and accuracy.

Construction of 2D/3D g-C3N4/BiOI Photocatalysts with p-n Heterojunction and Their Performance in Photocatalytic Degradation of Amaranth Dye.

The g-C3N4 (graphitic carbon nitride)/BiOI (bismuth oxyiodide) photocatalysts, boasting a unique nanomicrosphere architecture, were synthesized through a tripartite process involving heat polycondensation, hydrothermal treatment, and hybrid methods, using melamine, bismuth nitrate, and potassium iodide as starting materials. The photocatalyst was comprehensively characterized and analyzed while its efficacy in photocatalytic degradation of amaranth (AR) under various lighting conditions was investigated, and the catalytic mechanism was determined by kinetic analysis and free radical scavenging experiments. The results showed that g-C3N4 formed a strong bond with BiOI. The resulting composite catalyst retains the inherent 2D lamellar structure of g-C3N4, as well as the 3D microsphere structure of BiOI, thereby creating heterojunctions via p-n interactions. Under visible light exposure, g-C3N4/BiOI-15% demonstrated optimal catalytic performance, achieving a degradation rate of 74.64% for AR and exhibiting the highest rate constant. Radical tests confirmed that -O2- (superoxide anion) plays a crucial role as active species in the photocatalytic reaction.

Effect of aggregation configuration of molecular fluorophore CZA on photoluminescence properties of carbon dots.

The effect of aggregation configuration of molecular fluorophore citrazinic acid (CZA) on the photoluminescence (PL) properties of carbon dots (CDs) has been investigated using first-principles method. The structural stability of all aggregates has been analyzed, and the results show that the most stable structures are J-type CZA aggregates with head-to-tail configurations and the CZA/CD aggregates are bonded by replacing H atoms on the CD edges with de-OH from the pyridine ring of CZA. The luminescent properties of CZA/CD aggregates are mainly affected by the binding modes and binding sites. When the sites belong to electron-donating groups, electron-withdrawing groups or sp2 domain, the PL spectra of CDs are shifted and the luminescent intensities are significantly enhanced. The results suggest that covalently bonded CZA/CD aggregates are responsible for the high fluorescence quantum yield of CD. Moreover, the distance between the centers of the two pyridine rings in H-type CZA dimers less than 3.5 Å is prone to π-π stacking, leading to fluorescence quenching of aggregates. The present work is helpful in understanding the effect of molecular fluorophores on the PL properties of CDs and provides theoretical guidance for the controllable synthesis of CDs.