Reversing Immune Suppression and Potentiating Photothermal Immunotherapy via Bispecific Immune Checkpoint Inhibitor Loaded Hollow Polydopamine Nanospheres.

Despite the great achievements of immune checkpoint blockade (ICB) therapy on programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) axis, ICB monotherapy still faces obstacles in eradicating solid tumors due to the lack of tumor-associated antigens or tumor-specific cytotoxicity. Photothermal therapy (PTT) is a potential therapeutic modality because it can noninvasively kill tumor cells by thermal ablation and generate both tumor-specific cytotoxicity and immunogenicity, which holds great feasibility to improve the efficiency of ICB by providing complementary immunomodulation. Except for the PD-1/PD-L1 axis, the cluster of differentiation 47 (CD47)/signal regulatory protein alpha (SIRPα) pathway has been considered as a novel strategy of tumor cells to evade the surveillance of macrophages and inactivate the immune response of PD-L1 blockade therapy. Therefore, it is necessary to synergize the antitumor effect of dual-targeting PD-L1 and CD47. Although promising, the application of PD-L1/CD47 bispecific antibodies, especially in combination with PTT, remains a formidable problem, due to the low objective response, activity loss at relatively high temperature, or nonvisualization. Herein, instead of using antibodies, we use MK-8628 (MK) to down-regulate both PD-L1 and CD47 simultaneously through halting the active transcription of oncogene c-MYC, leading to elicitation of the immune response. The hollow polydopamine (HPDA) nanospheres are introduced as a biocompatible nanoplatform with high loading capacity and magnetic resonance imaging (MRI) ability to deliver MK and induce PTT (HPDA@MK). Compared to preinjection, HPDA@MK exhibits the strongest MRI signal at 6 h postintravenous injection to guide the precise combined treatment time. However, due to the local delivery and controlled release of inhibitors, HPDA@MK down-regulates c-MYC/PD-L1/CD47, promotes the activation and recruitment of cytotoxic T cells, regulates the M2 macrophages polarization in tumor sites, and especially boosts the combined therapeutic efficacy. Collectively, our work presents a simple but distinctive approach for c-MYC/PD-L1/CD47-targeted immunotherapy combined with PTT that may provide a desirable and feasible strategy for the treatment of other clinical solid tumors.

Sensitive lateral flow immunoassay strips based on Fe3+-chelated polydopamine nanospheres for the detection of kanamycin.

As kanamycin (KAN) residue in animal products is harmful to consumers, a rapid and sensitive method for KAN detection needs to be established. KAN monoclonal antibody (KAN-mAb, 1D11) with the half maximal inhibitory concentration of 1.16 ng/mL was prepared in this study. A one-pot method was used to synthesize Fe3+-chelated polydopamine nanospheres (Fe@PDANs) with excellent characteristics of strong light absorption. The novel label of Fe@PDANs and KAN-mAb was used to develop a lateral flow immunoassay (LFIA) for the sensitive detection of KAN. The limit of detection of the Fe@PDANs-based LFIA (Fe@PDANs-LFIA) for KAN was 0.0191 ng/mL, which was 2.75 times lower than PDANs-based LFIA. Furthermore, the Fe@PDANs-LFIA was successfully applied to detect KAN in pork, milk, and honey samples, with recoveries ranging from 93.75% to 113.80% (coefficient of variation < 10%). Therefore, Fe@PDANs have potential for the detection of analytes in LFIA.

Dual nucleases-assisted cyclic amplification using polydopamine nanospheres-based biosensors for one-pot detection of microRNAs.

The accurate detection of microRNAs (miRNAs) is essential in the early diagnosis and treatment of cancers. Existing miRNA detection methods represented by nucleic acid amplification (NAA) techniques, such as qRT-PCR, suffer from the small size of miRNAs and lead to limited practicability. CRISPR Cas13a system, another valuable toolbox for nucleic acid detection, relies heavily on the behaviors of accompanying isothermal NAA techniques, which prompts similar deficiencies in miRNA detection. In this study, a dual nucleases-assisted cyclic amplification (DUNCAN) strategy has been established to replace NAA techniques for one-pot detection of miRNAs. The DUNCAN strategy contained an initial reaction based on CRISPR Cas13a for target recognition, and an accompanied cyclic reaction using DNA probes protected by polydopamine nanospheres (PDANSs) for signal amplification and result readout. Exemplified by miR-19b, which has been confirmed to be related to several tumors, the quantitative detection through the DUNCAN strategy was achieved in the dynamic range of 10-106 fM, with a calculated detection limit of 1.27 fM. Besides, the DUNCAN strategy presented well selectivity and anti-interference performance for accurate detection of miR-19b in complex miRNA mixtures, different cell lines and clinical samples compared with qRT-PCR. All these performances demonstrated the promising potential of the DUNCAN strategy in clinical miRNA detection and diagnosis.

Molecular Dynamics Simulations of Polydopamine Nanosphere's Structure Based on Experimental Evidence.

In this work, we show how to obtain internal monodispersed gold nanoparticles inside polydopamine (PDA) nanospheres that are also externally decorated with gold. The number of internal nanoparticles is affected by the size of the PDA nanosphere used, and the lower limit in the number of gold nanoparticles in the center of decorated nanospheres, one single gold nanoparticle, has been reached. In addition, extensive molecular dynamics simulations of PDA nanospheres based on four different chemical motifs, in the presence of water and with different sizes, have been performed to gain insight into the arrangements capable of accommodating cavities. In particular, PDA nanospheres based on pyranoacridinotrione (PYR) units provide good agreement with the experimental attainment of internal metal nanoparticles. In these, the stacking of PYR units leads to a particular morphology, with large portions of space occupied by the solvent, that would explain the observed formation of gold nanoparticles inside the PDA nanosphere.

Polydopamine nanospheres-assisted direct PCR for rapid detection of Escherichia coli O157:H7.

Polymerase chain reaction (PCR) is one of the most common methods for rapid monitoring of foodborne pathogens; however, it requires purified nucleic acid as a template. Conventional nucleic acid purification is a time-consuming and laborious process. To overcome this, we developed polydopamine nanospheres (PDA NPs)-assisted direct PCR for detecting Escherichia coli O157:H7 (E. coli O157:H7). PDA NPs significantly enhanced PCR efficiency because of their strong interaction with PCR reagents, including polymerase and primers, thereby enabling regulation of the PCR performance. The optimal concentration and diameter for PDA NPs were 0.10 µg/µL and 504 nm, respectively. The PDA NPs-assisted direct PCR exhibited high sensitivity in E.coli O157:H7 detection. The detection limit of PDA NPs-assisted direct PCR was 6.7 × 104 CFU/mL, which was 10-fold lower than that of direct PCR (6.7 × 105 CFU/mL). Moreover, the sensor demonstrated excellent selectivity against E. coli O157:H7, with a negative reaction to eight other common pathogens. Most importantly, the PDA NPs-assisted direct PCR detected the order of 104-5 CFU/mL E.coli O157:H7 in milk, beef, and watermelon samples. No cultural enrichment was required, with the whole process taking <3 h. Therefore, PDA NPs-assisted direct PCR has tremendous potential in the rapid and sensitive detection of pathogens.

Polydopamine-based nanospheres as nanoplatforms to kill Staphylococcus aureus and to promote wound healing by photothermal therapy.

Bacterial infections have always been a threat when it comes to public health accounting for increased morbidity and mortality rates around the world. For the first time, Polydopamine is often used as an ocular surface drug delivery medium to treat some ocular surface diseases based on its good tissue affinity. Mesoporous polydopamine nanospheres (MPDA NPs) under photothermal therapy (PTT) are demonstrated as efficient therapeutic nanoplatforms for Staphylococcus aureus (S. aureus) infection and wound healing. MPDA NPs were found to exhibit excellent photothermal performance, significantly causing an increase in temperature within a short period of NIR-I exposure (808 nm, 1 W cm-2, 6 min). The MPDA NPs under the NIR irradiation remarkably eliminated S. aureus in vitro. Moreover, these synergistic effects turnouts to be phenomenal in vivo, effectively killing and healing S. aureus-infected abscesses in mice. These revealed the combined effect of the intrinsic antibacterial activity of MPDA NPs enhanced upon NIR-I exposure. Hence, MPDA NPs under NIR-I could prove excellent therapeutic nanoplatforms for bacteria-related infections and other biomedical applications.

Lateral flow immunoassay based on dual spectral-overlapped fluorescence quenching of polydopamine nanospheres for sensitive detection of sulfamethazine.

Herein, we propose a lateral flow immunoassay (LFIA) based on the dual spectral-overlapped fluorescence quenching of polydopamine nanospheres (PDANs) caused by the inner filter effect to sensitively detect sulfamethazine (SMZ). The fluorescence quenching LFIA device consists of four parts: absorbent pad, polyvinyl chloride pad, sample pad, and nitrocellulose membrane. Compared with traditional quenchers such as gold nanoparticles (AuNPs) with single spectral-overlapped quenching ability, PDANs can quench the excitation light and emission light of three fluorescence donors (aggregation-induced emission fluorescent microsphere, AIEFM; fluorescent microsphere, FM; and quantum dot bead, QB). The fluorescence intensity changes (ΔF) are numerically larger for PDANs-LFIA (ΔFAIEFM = 2315, ΔFFM = 979, ΔFQB = 910) than those for AuNPs-LFIA (ΔFAIEFM = 1722, ΔFFM = 833, ΔFQB =;520). AIEFM-based PDANs-LFIA exhibits a large ΔF (2315) in response to the changes in the SMZ concentration, and produces a high signal-to-noise ratio. The limit of detection (LOD) and visual LOD of LFIA based on PDANs quenching AIEFM for the detection of SMZ in chicken are 0.043 and 0.5 ng/mL, respectively. The results confirm that the proposed method can be used for the detection of hazardous materials in practical applications.

Hollow mesoporous polydopamine nanospheres: synthesis, biocompatibility and drug delivery.

Various polydopamine (PDA) nanospheres were synthesized by utilizing triblock copolymer Pluronic F127 and 1,3,5-trimethylbenzene (TMB) as soft templates. Precise morphology control of polydopamine nanospheres was realized from solid polydopamine nanospheres to hollow polydopamine nanospheres, mesoporous polydopamine nanospheres and hollow mesoporous polydopamine nanospheres (H-MPDANSs) by adjusting the weight ratio of TMB to F127. The inner diameter of the prepared H-MPDANSs can be controlled in the range of 50-100 nm, and the outer diameter is about 180 nm. Furthermore, the thickness of hollow mesoporous spherical shell can be adjusted by changing the amount of dopamine (DA). The H-MPDANSs have good biocompatibility, excellent photothermal properties, high drug loading capacity, and outstanding sustainable drug release properties. In addition, both NIR laser irradiation and acid pH can facilitate the controlled release of doxorubicin (DOX) from H-MPDANSs@DOX.

Polydopamine nanospheres with multiple quenching effect on TiO2/CdS:Mn for highly sensitive photoelectrochemical assay of tumor markers.

A photoelectrochemical (PEC) immunosensing strategy based on the multiple quenching of polydopamine nanoparticles (PDA NPs) to Mn2+-doped CdS-modified TiO2 nanoparticles (TiO2/CdS:Mn) was designed for the highly sensitive detection of carcinoembryonic antigen (CEA). The uniform PDA NPs possessed good dispersibility, good biocompatibility, and abundant functional groups for biomolecule assembly. They also had unique photophysical properties, with light absorption spanning the visible to infrared light range. When the immune-recognition brought the PDA NPs close to the TiO2/CdS:Mn interface, the PDA NPs competed with TiO2/CdS:Mn to absorb light, consumed photoelectrons generated in the TiO2/CdS:Mn, and hindered the access of electron donors to photoactive materials. The contribution from these aspects thus led to a significant decrease in photocurrent. Benefiting from the multiple quenching mechanism, the PEC immunosensor showed high sensitivity for CEA detection. Under optimal conditions, a low detection limit of 0.02 pg/mL and a wide linear relationship from 0.1 pg/mL to 100 ng/mL were obtained. The immunoassay showed good reproducibility and stability, and good selectivity and high accuracy in serum sample analysis. In this regard, PEC immunosensors may have great application potential for screening tumor markers and the prevention and monitoring of serious diseases.

Selective extraction of perfluorooctane sulfonate in real samples by superparamagnetic nanospheres coated with a polydopamine-based molecularly imprinted polymer.

Superparamagnetic core-shell structured molecularly imprinted polydopamine nanospheres were constructed via self-polymerization of dopamine to attach the template onto the surface of magnetic Fe3 O4 substrate in tris-HCl solution. Then they were used for the specific recognition and extraction of perfluorooctane sulfonate from environmental water and human serum samples. The structural features and morphological characterization of the magnetic imprinting nanospheres were assessed, indicating that the magnetic polydopamine imprinted composite was successfully prepared and featured excellent magnetic separation characteristics. Adsorption experiments revealed that the magnetic adsorbents exhibited rapid adsorption kinetics and highly selective recognition properties toward perfluorooctane sulfonate. The stability and regeneration experiments indicated the materials had repeatable activity retention after repeated reuse. As a magnetic solid-phase extraction adsorbent, it was successfully applied for the extraction and quantification of perfluorooctane sulfonate in environmental water and human serum samples combined with liquid chromatography tandem mass spectrometry, with recoveries of ∼70-101.5% obtained in real samples. These results demonstrate that the prepared magnetic imprinting nanospheres are effective for the selective separation of perfluorooctane sulfonate from real samples. The synthesis technique is an effective and facile method that is conducted in aqueous solution and at ambient temperature, which is low cost, environmentally benign, and easy for scaling-up.

Size-Dependent Modulation of Polydopamine Nanospheres on Smart Nanoprobes for Detection of Pathogenic Bacteria at Single-Cell Level and Imaging-Guided Photothermal Bactericidal Activity.

Pathogenic bacterial fouling in agriculture and food-associated products poses mounting food safety concerns today. Efficient integration of precise tracking and on-demand bacterial killing to achieve the source control of pathogenic bacteria at the single-cell level is one of the most valuable antifouling methods for safeguarding food safety but remains unexplored. Here, we report an all-in-one design strategy as a proof of concept to establish a stimuli-responsive nanoprobe PDANSs-FAM-Apt for the detection of Staphylococcus aureus (S. aureus) at the single-cell level, which could be capable of guiding the on-demand photothermal killing of bacteria upon near-infrared (NIR) light irradiation. By examining the size-dependent modulation of the fluorescence resonance energy transfer efficiency to polydopamine nanospheres (PDANSs), PDANSs-FAM-Apt was finally assembled by 6-carboxyfluorescein-terminated S. aureus, binding the aptamer (FAM-Apt) and PDANSs at ∼258 nm through π-π stacking interactions. As a result, PDANSs-FAM-Apt exhibits a remarkable fluorescence enhancement (∼261-fold) to S. aureus with a satisfactory detection limit of 1.0 cfu/mL, allowing for assay at the single-cell level and thus ultralow background fluorescence imaging of S. aureus as well as its biofilms. Moreover, PDANSs-FAM-Apt shows a high photothermal bactericidal property upon NIR light irradiation, endowing it with the strong capacity to efficiently produce heat for destroying S. aureus and its biofilms with the guidance of imaging results. This work emphasizes the versatility of using the combination of stimuli-responsive fluorescence imaging dependent on the PDANS size modulation and NIR light-activated photothermal antibacterial activity to design stimuli-responsive nanoprobes with an improved precision for pathogenic bacteria monitoring and source controlling, which opens a promising antifouling avenue to eliminate bacteria and disrupt bacterial biofilms in agriculture and food-related industries.

Self-assembled gold decorated polydopamine nanospheres as electrochemical sensor for simultaneous determination of ascorbic acid, dopamine, uric acid and tryptophan.

Herein, a new sensor based on screen-printed carbon electrodes covalently modified with self-assembled gold-decorated-polydopamine nanospheres (Au-PDNs) is reported. The sensor was applied to the simultaneous determination of the biologically significant molecules ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (TR). The Au-PDNs were anchored to gold nanoparticles electrodeposited onto the bare electrodes via cysteamine-glutaraldehyde bridges, and were characterized by scanning and transmission electron microscopies. The stepwise fabrication of the electrodes and their electrochemical responses were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry. The response of the new device to these analytes is pH-dependent, which allows selecting the best working conditions as a function of the sample characteristics. At pH values of 3.0 and 8.0, it was possible to determine simultaneously AA, UA and TR in presence of DA, and DA, UA and TR in presence of AA respectively, with very wide linear ranges and high sensitivities. The simultaneous determination of AA, DA, UA and TR was possible at pH 6.0 with competitive sensitivities in two consecutive linear ranges, between 10-80 µM and 80-240 µM; 1-160 µM and 160-350 µM; 10-120 µM and 120-350 µM; and 1-160 µM and 160-280 µM, respectively. The obtained limits of detection were 0.2 nM, 0.1 nM, 0.1 nM and 0.1 nM, respectively.

Polydopamine nanospheres as high-affinity signal tag towards lateral flow immunoassay for sensitive furazolidone detection.

Currently, the low sensitivity and poor binding stability of detection probe prepared via electrostatic adsorption have become the dilemmas of colloidal gold-based lateral flow immunoassays (Au-LFIAs). In this connection, polydopamine nanospheres (PDA NPs) with an eminent covalent connectivity property were introduced as a promising substitute to improve the stability of probe and sensitivity of LFIA. Whereafter, the PDA NPs-based LFIA was applied for the monitoring of furazolidone (FZD) in food samples because of the potential carcinogenic/mutagenic effects to human of its metabolite (3-amino-2-oxazolidinone, AOZ). Compared with electrostatic adsorption, the binding stability of PDA NPs-based probes was superior. And, as expected, the PDA NPs-based LFIA biosensor exhibited higher sensitivity than that of the Au-LFIA with a detection limit of 3.5 ng mL-1 for AOZ by naked-eye readout. Based on the significant enhanced binding stability and sensitivity, the PDA NPs-based LFIA is of certain spreading value for detecting other analytes.

Colistin-Loaded Polydopamine Nanospheres Uniformly Decorated with Silver Nanodots: A Nanohybrid Platform with Improved Antibacterial and Antibiofilm Performance.

Bacterial infections, especially chronic infections caused by bacterial biofilms, have become a worldwide threat to public health. Encouragingly, the synergistic actions of two or more antibacterial drugs have been proven to be effective in treating refractory bacterial infections. Herein, we fabricated a robust antibacterial nanohybrid, the colistin-loaded polydopamine nanospheres (PDA NSs) decorated uniformly with small silver nanodots (u-CPSs), and the u-CPSs could realize synergistic bactericidal performance for combating bacterial infections. PDA NSs, as an adhesive nanocarrier, could bind to the bacterial surfaces, where the drugs (colistin and silver ions) on the PDA surfaces could be released persistently via a near-infrared laser-triggered manner. Interestingly, compared with colistin-loaded PDA NSs decorated sparsely with large silver nanoparticles (s-CPSs), the u-CPSs exhibited stronger antibacterial and antibiofilm effects. We have also demonstrated that the u-CPSs could disrupt the cell walls/membranes of Gram-negative Escherichia coli bacteria and induce the generation of toxic reactive oxygen species within the bacteria. Collectively, the present work exemplifies the exquisite design and synthesis of PDA-based nanohybrids for achieving synergistic antibacterial and antibiofilm activities, which may promote the development of more powerful nanoagents to fight against bacterial infections.

Bioinspired sensor chip for detection of miRNA-21 based on photonic crystals assisted cyclic enzymatic amplification method.

Cancer, as the most invasive disease in the world, has led to an increasing amount of death year by year, so it is highly desired to develop a portable device to monitor the aberrant expression of biomarker in cancer patient. Here, we present a bio-photonic periodic nanostructures sensor chip assisted cyclic enzymatic amplification method to detect miRNA-21 with a detection limit of 55 fM. By employing biocompatible polydopamine nanospheres (PDANs) and DNaseⅠto construct an target-recycling amplification process on the photonic crystals, the output fluorescence signal can be strengthened selectively and short amplification time is needed. Benefiting from the synergy of the enhancement of photonic crystals and enzymatic cycle amplification, we realize high sensitivity detection of miRNA-21 with a detection range of 1 pM-10 nM and a detection limit of about four orders of magnitudes lower than the method employs no amplification, showing an expectable prospect in the early diagnosis of cancer.

Polydopamine nanospheres loaded with l-cysteine-coated cadmium sulfide quantum dots as photoelectrochemical signal amplifier for PSA detection.

A sandwich-type photoelectrochemical (PEC) immunosensor was constructed for sensitive detection of prostate specific antigen (PSA). It was based on electrochemically reduced graphene oxide-TiO2 (ERGO-TiO2) as photoelectrochemical platform to immobilize capture antibody (Ab1). Then, quinone-rich polydopamine nanospheres (PDANS) loaded detection antibody (Ab2) and photocurrent signal label, l-cysteine-coated cadmium sulfide quantum dots (CdSQDs). ERGO-TiO2 displayed greatly improved photocurrent response to white light. CdSQDs conjugated with PDANS further amplified photocurrent signal because of the good conductivity of PDANS and ERGO. The increased photocurrent showed a linear correlation with PSA in the concentration range from 0.02 pg mL-1 to 200 ng mL-1 with the detection limit of 6.8 fg mL-1. It also revealed high selectivity and good stability.

Short duration cancer treatment: inspired by a fast bio-resorbable smart nano-fiber device containing NIR lethal polydopamine nanospheres for effective chemo-photothermal cancer therapy.

BACKGROUND: The objective of this study was to evaluate the efficacy of a combination of Photothermal therapy (PTT) and chemotherapy in a single nano-fiber platform containing lethal polydopamine nanopheres (PD NPs) for annihilation of CT 26 cancer cells. METHOD: Polydioxanone (PDO) nanofiber containing PD and bortezomib (BTZ) was fabricated via electrospinning method. The content of BTZ and PD after optimization was 7% and 2.5% respectively with respect to PDO weight. PD NPs have absorption band in near-infrared (NIR) with resultant rapid heating capable of inducing cancer cell death. The samples was divided into three groups - PDO, PDO+PD, and PDO+PD-BTZ for analysis. RESULTS: In combined treatment, PDO nanofiber alone could not inhibit cancer cell growth as it neither contain PD or BTZ. However, PDO+PD fiber showed a cell viability of approximately 20% after 72 hr of treatment indicating minimal killing via hyperthermia. In the case of PDO composite fiber containing BTZ, the effect of NIR irradiation reduced the viability of cancer cells down to around 5% after 72 h showing the efficiency of combination therapy on cancer cells elimination. However, due to higher photothermal conversion that may negatively affect normal cells above 46°C, we have employed 1 s "OFF" and 2 s "ON" after initial 9 s continuous irradiation to maintain the temperature between 42 and 46°C over 3 mins of treatment using 2 W/cm2; 808 nm laser which resulted to similar cell death. CONCLUSION: In this study, combination of PTT and chemotherapy treatment on CT 26 colon cancer cells within 3 min resulted in effective cell death in contrast to single treatment of either PTT and chemotherapy alone. Our results suggest that this nanofiber device with efficient heating and remote control drug delivery system can be useful and convenient in the future clinical application for localized cancer therapy.

Copper nanoclusters/polydopamine nanospheres based fluorescence aptasensor for protein kinase activity determination.

A fluorescence aptasensor was constructed for protein kinase (PKA) activity detection by utilizing copper nanoclusters (CuNCs) and polydopamine nanospheres (PDANS). Through the π-π stacking interactions between adenosine triphosphate (ATP) aptamer and PDANS, the ATP aptamer modified CuNCs (apt-CuNCs) were absorbed onto PDANS surface, thus the fluorescence of apt-CuNCs were quenched through fluorescence resonance energy transfer (FRET) from apt-CuNCs to PDANS. In the presence of ATP, ATP specifically bound to aptamer, causing the dissociation of apt-CuNCs from PDANS surface and restoring the fluorescence of apt-CuNCs. However, PKA translated ATP into adenosine diphosphate (ADP), and ADP had no competence to combine with ATP aptamer, thus, apt-CuNCs were released and absorbed onto the PDANS surface to cause the fluorescence quenching of apt-CuNCs again. Therefore, PKA activity was conveniently detected via the fluorescence signal change. Under the optimal conditions, PKA activity was detected in the range of 0.05-4.5 U mL-1 with a detection limit of 0.021 U mL-1. Furthermore, the feasibility of the aptasensor for kinase inhibitor screening was explored via assessment of kinase inhibitor H-89 as one model. This aptasensor was also performed for PKA activity determination in HepG2 cell lysates with satisfactory results.

Simultaneous determination of dopamine and uric acid in the presence of ascorbic acid using a gold electrode modified with carboxylated graphene and silver nanocube functionalized polydopamine nanospheres.

A voltammetric sensor is presented for the simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). It is based on a gold electrode (GE) modified with carboxyl-functionalized graphene (CFG) and silver nanocube functionalized DA nanospheres (AgNC@PDA-NS). The AgNC@PDA-NS nanocomposite was characterized by scanning electron microscopy and UV-Vis spectroscopy. The electrochemical behavior of the modified electrode was evaluated by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The modified electrode displays good electrocatalytic activity towards DA (typically at 0.14 V vs. Ag/AgCl) and UA (typically at 0.29 V vs. Ag/AgCl) even in the presence of ascorbic acid. Response to DA is linear in the concentration range of 2.5 to 130 µM with a detection limit of 0.25 µM. Response to UA is linear in the concentration range of 10 to 130 µM with a detection limit of 1.9 µM. In addition, the sensitivity for DA and UA is 0.538 and 0.156 µA µM-1 cm-2, respectively. The modified electrode also displays good stability, selectivity and reproducibility. Graphical abstract The gold electrode modified with polydopamine nanospheres functionalized with silver nanocube and carboxylated graphene is used for simultaneous determination of DA and UA in the presence of AA, with wide linear range and low detection limit.

Two-Way Reversible Shape Memory Polymers Containing Polydopamine Nanospheres: Light Actuation, Robotic Locomotion, and Artificial Muscles.

Two-way reversible shape memory polymers (2W-SMPs), especially those that are light-responsive, are highly desirable for many applications, especially in the biomedical field, because of the convenience of indirect heating. We have designed and prepared a series of light-actuated 2W-SMP composites by incorporating very small amounts of polydopamine (PDA) nanospheres into semicrystalline polymer networks based on biodegradable poly(ε-caprolactone) copolymers. PDA nanospheres can be well dispersed in chloroform and well mixed with the polymer network. PDA nanospheres manifest good photothermal effect because of their strong absorption of light. The variation in temperature of the polymer composites can be correlated with irradiation time, light intensity, and the content of PDA nanospheres. Equations are developed to fit the temperature changes of the materials as a function of irradiation power and of the PDA particles content for a better understanding of the kinetics of the light-to-heat conversion. These polymer composites show excellent two-way reversible shape memory effects (2W-SMEs) under stress-free condition when the light is switched on and off showing a reversible angle change of 45°. The speed of angle change is larger for polymer composites irradiated with a stronger light or with a higher content of PDA nanospheres. This is the first report on 2W-SMPs using incorporated PDA nanospheres as photothermal fillers. A moving robot is designed based on photoresponsive 2W-SMP composites, which can walk on a track with triangular saw-teeth. This composite is capable of lifting and lowering a weight, acting as artificial muscles, and its actuated stress is much higher than the maximum stress yielded by most mammalian skeletal muscles. The use of biodegradable polyesters and thermal fillers made of a natural compound dopamine makes such composites potentially useful as biomaterials.