Staphylococcus aureus dry-surface biofilms are more resistant to heat treatment than traditional hydrated biofilms

BACKGROUND

The importance of biofilms to clinical practice is being increasingly realized. Biofilm tolerance to antibiotics is well described but limited work has been conducted on the efficacy of heat disinfection and sterilization against biofilms.

AIM

To test the susceptibility of planktonic, hydrated biofilm and dry-surface biofilm forms of Staphylococcus aureus, to dry-heat and wet-heat treatments.

METHODS

S. aureus was grown as both hydrated biofilm and dry-surface biofilm in the CDC biofilm generator. Biofilm was subjected to a range of temperatures in a hot-air oven (dry heat), water bath or autoclave (wet heat).

FINDINGS

Dry-surface biofilms remained culture positive even when treated with the harshest dry-heat condition of 100°C for 60min. Following autoclaving samples were culture negative but 62-74% of bacteria in dry-surface biofilms remained alive as demonstrated by live/dead staining and confocal microscopy. Dry-surface biofilms subjected to autoclaving at 121°C for up to 30min recovered and released planktonic cells. Recovery did not occur following autoclaving for longer or at 134°C, at least during the time-period tested. Hydrated biofilm recovered following dry-heat treatment up to 100°C for 10min but failed to recover following autoclaving despite the presence of 43-60% live cells as demonstrated by live/dead staining.

CONCLUSION

S. aureus dry-surface biofilms are less susceptible to killing by dry heat and steam autoclaving than hydrated biofilms, which are less susceptible to heat treatment than planktonic suspensions.

One-Pot Synthesis of Carbon Nanodots in an Organic Medium with Aggregation-Induced Emission Enhancement (AIEE): A Rationale for "Enzyme-Free" Detection of Cholesterol

Addressing the limitations associated with the detection of cholesterol, we present a one-pot synthesis of a carbon nanodot (CD) in an organic medium (CD_org) from a novel bile acid hydrazone-based organogel. Interestingly, CD_org possesses the aggregation-induced emission enhancement (AIEE) phenomenon, which rationally aids in the "enzyme-free" detection of cholesterol through a fluorescence turn-on mechanism. On dilution of the THF/water mixture of CD_org with its poor solvent (water), a 9.8-fold enhancement in its photoluminescence (PL) emission is witnessed. Such an enhancement in PL emission is credited to the occurrence of molecular restrictions due to the formation of nanoaggregates of CD_org, thereby initiating a radiative pathway for exciton decay. Excitingly on adding cholesterol to CD_org, we observed a similar enhancement in its PL emission without the use of any cholesterol oxidase (ChO _x ) enzyme. The limit of detection and limit of quantification of cholesterol is found to be as low as 1.09 and 3.64 μM, respectively. Hence, this contribution highlights the enzyme-free fluorescence turn-on detection of cholesterol by a novel CD rationally designed to extend its applicability in an organic medium, where it is still considered a major restraint.

Chiral carbon dots and their effect on the optical properties of photosensitizers

In this work, we have successfully prepared intrinsically chiral carbon dots from chiral precursors. We have also demonstrated that the chirality of these carbon dots can affect the optical properties of photosensitizer molecules like azobenzene.

Carbon-Dot-Coated Alginate Beads as a Smart Stimuli-Responsive Drug Delivery System

In this work, we report a smart stimuli-responsive drug delivery system (DDS) that can release drug depending upon the amount of pathogen (MRSA) present in the target. A greater amount of MRSA in the system will lead to more release of drug and vice versa. Carbon-dot-coated novel alginate beads (CA-CD) exhibiting superior stability was successfully used as smart drug delivery vehicle. Garlic extract (GE), which contains allicin, was taken as model drug system to demonstrate the phenomena. It was observed that GE loading was 19 and 78% with CA and CA-CD, respectively. CA-CD-GE shows pH-dependent controlled drug release, which results in increased therapeutic efficiency. CA-CD-GE is not only stimuli responsive but also a controlled drug release system as it releases drug according to the pathogen concentration (MRSA). All the three factors viz. drug release, MRSA concentration and pH of the medium are interdependent as when the cell divides, it produces secondary metabolites that lead to the decrease in pH of the medium. The drop in the pH value triggers drug release from the beads. And the effect of the drug is reflected by the MRSA cell death. Hence, we demonstrate a smart stimuli responsive DDS. However, such DDS will be useful in cases where increased amount of pathogen in the system will lead to reduction in pH.

Chitosan-Iron Oxide Coated Graphene Oxide Nanocomposite Hydrogel: A Robust and Soft Antimicrobial Biofilm

We report a robust biofilm with antimicrobial properties fabricated from chitosan-iron oxide coated graphene oxide nanocomposite hydrogel. For the first time, the coprecipitation method was used for the successful synthesis of iron oxide coated graphene oxide (GIO) nanomaterial. After this, films were fabricated by the gel-casting technique aided by the self-healing ability of the chitosan hydrogel network system. Both the nanomaterial and the nanocomposite films were characterized by techniques such as scanning electron microscopy, FT-IR spectroscopy, X-ray diffraction, and vibrating sample magnetometry. Measurements of the thermodynamic stability and mechanical properties of the films indictaed a significant improvement in their thermal and mechanical properties. Moreover, the stress-strain profile indicated the tough nature of the nanocomposite hydrogel films. These improvements, therefore, indicated an effective interaction and good compatibility of the GIO nanomaterial with the chitosan hydrogel matrix. In addition, it was also possible to fabricate films with tunable surface properties such as hydrophobicity simply by varying the loading percentage of GIO nanomaterial in the hydrogel matrix. Fascinatingly, the chitosan-iron oxide coated graphene oxide nanocomposite hydrogel films displayed significant antimicrobial activities against both Gram-positive and Gram-negative bacterial strains, such as methicillin-resistant Staphylococcus aureus, Staphylococcus aureus, and Escherichia coli, and also against the opportunistic dermatophyte Candida albicans. The antimicrobial activities of the films were tested by agar diffusion assay and antimicrobial testing based on direct contact. A comparison of the antimicrobial activity of the chitosan-GIO nanocomposite hydrogel films with those of individual chitosan-graphene oxide and chitosan-iron oxide nanocomposite films demonstrated a higher antimicrobial activity for the former in both types of tests. In vitro hemolysis potentiality tests and MTT assays of the nanocomposite films indicated a noncytotoxic nature of the films, which conveyed the possibility of potential applications of these soft and tough films in biomedical as well as in the food industry.

A sulphonated carbon dot-chitosan hybrid hydrogel nanocomposite as an efficient ion-exchange film for Ca2+ and Mg2+ removal

We have developed a hybrid hydrogel nanocomposite film via conjugation of oxidised carbon dots synthesized from 11-mercaptoundecanoic acid with chitosan. The potential applicability of the film was then successfully tested for the removal of Ca2+ and Mg2+ ions from solution.

Functionalized graphene oxide quantum dot-PVA hydrogel: a colorimetric sensor for Fe²⁺, Co²⁺ and Cu²⁺ ions

Functionalized graphene oxide quantum dots (GOQDs)-poly(vinyl alcohol) (PVA) hybrid hydrogels were prepared using a simple, facile and cost-effective strategy. GOQDs bearing different surface functional groups were introduced as the cross-linking agent into the PVA matrix thereby resulting in gelation. The four different types of hybrid hydrogels were prepared using graphene oxide, reduced graphene oxide, ester functionalized graphene oxide and amine functionalized GOQDs as cross-linking agents. It was observed that the hybrid hydrogel prepared with amine functionalized GOQDs was the most stable. The potential applicability of using this solid sensing platform has been subsequently explored in an easy, simple, effective and sensitive method for optical detection of M(2+) (Fe(2+), Co(2+) and Cu(2+)) in aqueous media involving colorimetric detection. Amine functionalized GOQDs-PVA hybrid hydrogel when put into the corresponding solution of Fe(2+), Co(2+) and Cu(2+) renders brown, orange and blue coloration respectively of the solution detecting the presence of Fe(2+), Co(2+) and Cu(2+) ions in the solution. The minimum detection limit observed was 1 × 10(-7) M using UV-visible spectroscopy. Further, the applicability of the sensing material was also tested for a mixture of co-existing ions in solution to demonstrate the practical applicability of the system. Insight into the probable mechanistic pathway involved in the detection process is also being discussed.

Ethylene diamine mediated cobalt nanoparticle studded graphene oxide quantum dots with tunable photoluminescence properties

The present study demonstrates ethylene diamine mediated in situ synthesis of cobalt oxide nanoparticles (Co₃O₄NPs) studded on graphene oxide quantum dots (GOQDs) showing reversible on/off fluorescence switching.

Paper carbon dot based fluorescence sensor for distinction of organic and inorganic sulphur in analytes

In this work a paper carbon dot (PCDs) based fluorescence sensor was developed which can distinguish between the organic and inorganic sulphur in analytes.

Amino acid appended cholic acid–azobenzene dyad: an effective & smart phase selective gelator for aromatic solvents

A series of amino acid appended cholic acid–azobenzene dyads have been synthesized and studied for their phase selective gelation behavior, which was further explored for water purification and oil spill remediation.

Carbon dots rooted agarose hydrogel hybrid platform for optical detection and separation of heavy metal ions

A robust solid sensing platform for an on-site operational and accurate detection of heavy metal is still a challenge. We introduce chitosan based carbon dots rooted agarose hydrogel film as a hybrid solid sensing platform for detection of heavy metal ions. The fabrication of the solid sensing platform is centered on simple electrostatic interaction between the NH3+ group present in the carbon dots and the OH- groups present in agarose. Simply on dipping the hydrogel film strip into the heavy metal ion solution, in particular Cr6+, Cu2+, Fe3+, Pb2+, Mn2+, the strip displays a color change, viz., Cr6+→yellow, Cu2+→blue, Fe3+→brown, Pb2+→white, Mn2+→tan brown. The optical detection limit of the respective metal ion is found to be 1 pM for Cr6+, 0.5 μM for Cu2+, and 0.5 nM for Fe3+, Pb2+, and Mn2+ by studying the changes in UV-visible reflectance spectrum of the hydrogel film. Moreover, the hydrogel film finds applicability as an efficient filtration membrane for separation of these quintet heavy metal ions. The strategic fundamental feature of this sensing platform is the successful capability of chitosan to form colored chelates with transition metals. This proficient hybrid hydrogel solid sensing platform is thus the most suitable to employ as an on-site operational, portable, cheap colorimetric-optical detector of heavy metal ion with potential skill in their separation. Details of the possible mechanistic insight into the colorimetric detection and ion separation are also discussed.

Property relationship of alginate and alginate–carbon dot nanocomposites with bivalent and trivalent cross-linker ions

Biocompatible alginate and alginate–carbon dot nanocomposites with superior properties and good mechanical properties.

Magnetic alginate–Fe3O4 hydrogel fiber capable of ciprofloxacin hydrochloride adsorption/separation in aqueous solution

Magnetic alginate–Fe₃O₄ hydrogel fibers were successfully prepared and used as adsorption/separation of ciprofloxacin hydrochloride using a simple laboratory micropipette, employing the basic principle of the wet spinning technique.

Fragmentation of supported gold nanoparticles@agarose film by thiols and the role of their synergy in efficient catalysis

A non-conventional fragmentation of supported gold nanoparticles@agarose film by thiols through a prompt electron transfer is demonstrated. The film also shows catalysis of p-nitrophenol reduction in only ∼20 to 30 s.

β-Cyclodextrin and calix[4]arene-25,26,27,28-tetrol capped carbon dots for selective and sensitive detection of fluoride

In this work we have designed a novel system based on carbon dots prepared from chitosan gel capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol for sensitive and selective detection of fluoride ions in aqueous media. Fluorescent carbon dots prepared from chitosan gel when capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol results in quenching of its fluorescence intensity. Introduction of F(-) ions to carbon dots capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol system results in enhancement and restoration of fluorescence intensity leading to detection of F(-) ion. Minimum detection limit was determined to be ∼6.6 μM. The detection is selective as with other halide ions i.e. Cl(-), Br(-) and I(-) and hydroxyl ion (OH(-)), there is observed decrease of fluorescence intensity. A possible mechanism to justify the observation is also discussed in the paper.

Green chitosan-carbon dots nanocomposite hydrogel film with superior properties

In this work we report novel chitosan-carbon dots nanocomposite hydrogel films. A new green source "tea" was used as precursor for carbon dots (CDs). The electrostatic interaction of positive charge on chitosan and negative charge on CDs prepared from tea was used for the successful preparation of a stable and robust chitosan-carbon dots nanocomposite hydrogel film. The hydrogel films were characterized by UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FTIR), scanning electron microscope (SEM), fluorescent microscopy, thermogravimetric analysis (TGA) and contact angle analysis. It was observed that chitosan-carbon dots hydrogel films are soft but tough with superior UV-visible blocking, swelling, thermal and mechanical properties in comparison to chitosan hydrogel film. Moreover chitosan-carbon dots films are more water repellent (hydrophobic) as indicated by their high contact angle values. Thus, fabrication of such green soft but tough biocompatible chitosan-carbon dots nanocomposite hydrogel films offers tremendous bio-medical and industrial applications.

In-situ and ex-situ chitosan-silver nanoparticle composite: comparison of storage/release and catalytic properties

In this work storage of silver nanoparticles (Ag NPs) in chitosan gel and its subsequent release for catalytic reduction processes is investigated. The generation of small sized metal nanoparticles which acts as catalyst is prerequisite to progress of a catalytic reaction. We show that Ag NPs extracted from chitosan gel are less than 5 nm so very effective in catalysis. Chitosan-Ag nanocomposite gels were prepared from two different approaches. The first approach involves in-situ incorporation of Ag nanoparticles into the reaction mixture while preparing the chitosan hydrogel and termed as chitosan-Ag-in-situ (CH-Ag-I) nanocomposite gel. And, in second approach already prepared chitosan hydrogel was placed in Ag NPs solutions, resulting in adsorption of Ag NPs and thus forming chitosan-Ag-ex-situ (CH-Ag-E) nanocomposite gel. The prepared gels were characterized by UV-Visible spectroscopy, Fourier transformed infra-red spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Scanning electron microscopy (SEM). Swelling studies showed that the CH-Ag-E exhibits efficient water absorption property compared to that of CH-Ag-I. In addition to efficient swelling properties the CH-Ag-E can also act as store house of Ag NPs that can be used to catalyze the reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP) as Ag NPs of this composite can be easily extracted just by treating with sodium borohydride which is not possible in case of CH-Ag-I. The rate of the reaction increases upto 10 fold when CH-Ag-E nanocomposite gel is used as catalyst in comparison to CH-Ag-I. The reduction reaction catalyzed by such Ag NPs follow zero order kinetics and dependent on the size of the Ag NPs loaded in the gel (CH-Ag-E) as well as on the amount of the gel used. We found that smaller is the size of the loaded Ag NPs in CH-Ag-E, more effective it is in catalyzing the reduction reaction. The CH-Ag-E gel also showed reusability with efficient catalysis.

Novel carbon dot coated alginate beads with superior stability, swelling and pH responsive drug delivery

Novel carbon dot coated alginate beads (CA-CD) exhibiting superior stability and swelling properties have been successfully prepared. CA-CD show exceptional stability in ambient condition and are stable at room atmosphere and temperature even after 60 days. Moreover, CA-CD show excessive swelling in comparison to calcium alginate (CA) beads. The beads were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and optical microscopy. The CA and CA-CD beads were investigated for their use as pH dependent sustained drug delivery vehicles taking tetracycline (TC) and tetracycline associated with β-cyclodextrin (β-TC) as model drug systems. It was observed that TC loading was 35% and 77% with CA and CA-CD, respectively. Tetracycline associated with β-cyclodextrin (β-TC) shows 48% loading for CA and much greater loading (as high as 90%) for CA-CD. At pH 1, CA-CD and CA beads show maximum drug release with TC cumulative release of 70% and 37% at 96 h, respectively. However, the delivery rates at pH 1 were slower in case of tetracycline associated with β-cyclodextrin (β-TC) loading showing 61% release for CA-CD and 22% for CA after 96 h. Thus, CA-CD can be suitably used as an effective drug delivery vehicle with maximum release obtained at pH 1 emphasizing its use in the gastrointestinal tract where pH is low. Also, the use of β-cyclodextrin with the drug as an inclusion complex renders the CA and CA-CD beads useful for slow and long-term drug administration.

Evaluation of ophthalmic manifestations in patients with intracranial tumours

The present study was done to observe the ophthalmic manifestations in patients with intracranial tumor. This was a prospective, purposive, consecutive, observational study conducted in patients with radiologically proven intracranial tumors in the department of Ophthalmology with collaboration of Department of Neuro-surgery of Bangabandhu Sheikh Mujib Medical University from January 2006 to December 2010. All cases had tissue histopathology confirmation post-operatively. The most common type of intracranial tumor was pituitary adenoma (58.04%), followed by craniopharyngioma (20.53%), posterior fossa tumour (12.50%) [medulloblestoma, ependymoma], meningioma (8.04%) [sphenoidalwing meningioma, petroclavel meningioma, oligodendroglioma] and others (0.89%) [nasopharyngial carcinoma, esthesio - astrocytoma]. Common neuro-ophthalmological findings were visual blur (91.07%), visual field defect (71.42%), optic disc changes (50%), pupillary light reaction defect (48.21%) and colour vision defect (46.42%). The study shows, pituitary adenoma is the most common tumor that impairs the visual pathway structures followed by craniopharyngioma, posterior fossa tumour & meningioma. Furthermore, decreased visual acuity, visual field defect, abnormal optic discs, relative afferent pupillary defect and ophthalmoplegia etc. are the common neuro-ophthalmic features that should be carefully examined for early detection of intracranial tumors.

The impact of cerebral embolization during infant cardiac surgery on neurodevelopmental outcomes at intermediate follow-up

Cerebral embolization during pediatric cardiac surgery may be an underappreciated source of subsequent neurodevelopmental impairment. Transcranial Doppler ultrasound is a neuromonitoring tool that can provide intraoperative surveillance for cerebral embolization. We hypothesized that increased cerebral embolic signals detected during infant cardiac surgery would be associated with worse neurodevelopmental outcomes at follow-up. A study group of 24 children who underwent infant cardiac surgery with transcranial Doppler detection of cerebral embolic signals returned at intermediate follow-up for standardized neurodevelopmental assessment. The children were evaluated using two neurocognitive tests and the parents completed two questionnaires regarding observed behavior. Statistical analysis assessed for correlation between the number of cerebral embolic signals at surgery and the results of the neurodevelopmental assessment. Of the 67 test parameters analyzed, five showed a significant association with the number of embolic signals, yet, all in the contrary direction of the clinical hypothesis, likely representing a Type I error. Thus, in this small cohort of patients, the number of cerebral embolic signals detected during infant cardiac surgery was not shown to be associated with worse neurodevelopmental outcomes at intermediate follow-up. A larger study is probably necessary to ascertain the potential influence of cerebral embolic signals on eventual neurologic outcomes in children. The clinical relevance of cerebral embolic signals during pediatric cardiac surgery remains undetermined and deserves further investigation.