Synthesis, characterization and antimicrobial properties of silver phthalocyanine-silver (AgPc-Ag) supported on aminosilane-modified silicate

doi:10.21203/rs.3.rs-4160231/v1

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Synthesis, characterization and antimicrobial properties of silver phthalocyanine-silver (AgPc-Ag) supported on aminosilane-modified silicate

https://doi.org/10.21203/rs.3.rs-4160231/v1

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Organic–inorganic composite antibacterial materials based on AgPc/Ag and aminosilane-modified silicate (Ormosil) were prepared by sol-gel processes and an in situ reduction method. The physical and chemical properties of AgPc, Pc-Ormosil and AgPc-Ormosil/Ag composites were analyzed by SEM, XRD, NMR and XPS spectroscopy. As a result, Ag nanoparticles were bonded and chelated in Pc-Ormosil matrix. The morphology analysis of SEM showed that the AgNPs in the Pc-Ormosil matrix were spherical and uniformly distributed, with a size of about 5–10 nm. These NMR and XPS results indicated that the AgNPs were coordinated with Pc (N–Ag–N) and chelated with Ormosil (–CH₂NH…Ag and Si–OH…Ag) to form a AgPc-Ormosil/Ag composite. The antibacterial effects of AgPc-Ormosil/Ag composites on Gram-negative Pseudomonas aeruginosa and Escherichia coli, and Gram-positive Staphylococcus aureus and Bacillus subtilis were evaluated by inhibiting ring, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and plate counting, and excellent antibacterial properties were obtained.

Antibacterial material

Silver phthalocyanine

Minimum inhibitory concentration

Minimum bactericidal concentration

Aminosilane-modified silicate (Ormosil) is an organic-inorganic hybrid material formed by hydrolysis and condensation of organic-modified silane and alkoxide precursor. Ormosil materials are an important area of research in materials science, as they have been found to have many promising applications in the fields of optics, electronics, mechanics, energy, environment, biology, and medicine [1–4]. Ormosils have been shown to be excellent hosts for the capture of metal nanoparticles due to their ability to act as stabilizers or surface-capping agents [5, 6]. When metal nanoparticles are embedded or chelated in Ormosil, Ormosil is able to control nucleation to terminate particle growth [7]. Silver nanoparticles (AgNPs) have attracted much attention due to their ease of synthesis, chemical stability, and antimicrobial properties. A widely used method for AgNP synthesis is the reduction of Ag ions in aqueous solution in the presence of a capping agent, such as aminosilane molecules, which stabilize the AgNPs as they have a free amino group available to couple the free AgNPs, preventing AgNP aggregation through chelation forces [8].

Silver and silver-based antimicrobials have become the focus of research, not only because active Ag⁺ is non-toxic to human cells, but also because of their high temperature stability and low volatility, which can be used as new properties of long-acting fungicides. Silver ions are important antimicrobial agents due to their antiseptic properties, and only a few bacteria are intrinsically resistant to this metal [9–11]. Phthalocyanine (Pc) is a highly effective photosensitizer and has been successfully used in photodynamic therapy. Photodynamic therapy utilizes visible light, molecular oxygen, and photosensitizers to kill cells [12, 13]. The literature reports that a related therapy called photodynamic antimicrobial chemotherapy (PACT) has been studied for the treatment of diseases caused by bacteria. The combination of Pcs with AgNPs may increase biological inactivation due to the combination of PACT (which utilizes the photosensitivity capacity of Pcs) and AgNPs alone (which have antimicrobial properties) [14]. Therefore, in this work, we investigated the inactivation of Gram-negative and Gram-positive bacteria by conjugates of Pcs with AgNPs.

Chelate AgNPs with Pc, glutathione, and aminosilanes has previously been reported [15, 16, 8]. They are used to stabilize AgNPs because they have free amino groups that can be used to conjugate AgNPs. The purpose of this work is to apply and optimize the sol-gel method to prepare AgPc and Ag by bonding and complex incorporation into the Ormosil network, to prepare AgPc-Ormosil/Ag complexes and to study the properties and antimicrobial properties of this new material. In this paper, the preparation process and structural properties of AgPc and Ag loaded on aminosilane-modified silicate AgPc-Ormosil/Ag are introduced, in which AgNPs are covalently bonded with Pcs and chelated with the Ormosil network. Pc-Ormosil composites were obtained by copolymerizing the reactive groups present in the aromatic ring of tetrachlorosulfonyl phthalocyanine (PcSO₂Cl) with N-[3-(trimethoxysilyl) propyl] diethylenetriamine (ATS) by sol-gel process. Then, AgNPs were immobilized in Pc and aminosilanes, and Ormosil composites were prepared to promote the growth of AgPc-Ormosil/Ag network structure. In this study, the structural properties, physical properties and antimicrobial activity of the composites were analyzed. The inhibitory effect of AgPc-Ormosil/Ag composites against Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and Gram-positive Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis) was detected by inhibition zone test, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBCs) and plate counting method, respectively. As a feasibility assessment for future application in antimicrobial fabrics.

2.1 Materials and apparatus

TEOS, ATS, silver nitrate (AgNO₃) and 29H,31H-phthalocyanine (Pc) were purchased from Aldrich. Chlorosulfonic acid (ClSO₃H), anhydrous Na₂CO₃, dichloromethane, HCl and N₂H₄ were purchased from Merck. The formation and molecular structure of AgPc and AgPc-Ormosil/Ag composites were demonstrated by ¹³C and ²⁹Si NMR (MSL-400, Bruker) spectrophotometry and X-ray photoelectron spectroscopy (XPS, VG Scientific ESCALAB 250, UK). The NMR spectra of composite solid samples were obtained by cross-polarization/magic-angle spinning (CP-MAS) analysis. Tⁱ and Qⁱ denote a molecular structure with one and no organic side groups, respectively, while i refers to the number of -OSi- groups bound to silicon atoms. The microscopic topography of the composites was obtained using a scanning electron microscope (SEM, JSM-7600F). Phase identification of the composites was performed using X-ray diffraction (XRD; Siemens D5000) with Cu Kα radiation.

2.2 Preparation of AgPc and AgPc-Ormosil/Ag composites

Pc (5.0 mmol) and ClSO₃H (225 mmol) were refluxed at 110°C under N₂ for 5 h, and the solution was poured on crushed ice, extracted with methylene chloride, dried with Na₂CO₃, and the solvent was removed by rotary evaporation to prepare Pc-(SO₂Cl)₄[17]. The preparation of the AgPc composites is shown in Fig. 1. Place Pc-(SO₂Cl)₄ (5.0 mmol) in a round-bottom flask equipped with a stirrer, add 10 mL of pyridine and pass N₂ and stir for 30 min. Then add AgNO₃ solution and dilute hydrazine monohydrate aqueous solution, and continue to stir in an inert atmosphere at 60°C for 4 hours. The sol solution was then poured onto a polytetrafluoroethylene plate and placed in a 120°C drying oven for 12 h to obtain the AgPc composite.

The preparation of Pc-Ormosil and AgPc-Ormosil/Ag composites is shown in Fig. 1. Place Pc-(SO₂Cl)₄ (5.0 mmol) in a round-bottom flask equipped with a stirrer, add 10 mL of pyridine and pass N₂ and stir for 30 min. After adding ATS (25 mmol)/CH₂Cl₂ (50 mL) solution and stirring for 2 hours, add TEOS (25 mmol)/H₂O (50 mL) of dilute aqueous solution to the solution and continue stirring at 40°C under N₂ for 2 hours. An acid-catalyzed process using ATS and TEOS as the precursors was used to prepare the Ormosil solution. Quantitative AgNO₃ (weight ratios 1:0.1, 1:0.05 and 1:0.025 with respect to ATS + TEOS) was dissolved in 50 mL of an aqueous dispersion solution containing 10 wt.% N₂H₄. The resulting solution was added to the above-described Pc-(SO₂Cl)₄/ATS/TEOS sol solution, and stirring was continued under N₂ at 60°C for 12 h. The sol solution was then cast onto a polytetrafluoroethylene plate and placed in a drying oven at 50°C for 12 h, and the AgPc-Ormosil/Ag composites were finally obtained by heat-treating the dried films at 110°C for 2 h. The corresponding composites were designated AgPc-Ormosil/Ag-2.5, AgPc-Ormosil/Ag-5, and AgPc-Ormosil/Ag-10, respectively, according to the AgNO₃ content in the Pc-Ormosil composite.

2.3 Test of antibacterial properties

P. aeruginosa (ATCC 27853), E. coli (ATCC 25922), S. aureus (ATCC 25923), and B. subtilis were used as reference strains for antimicrobial trials from Taiwan Food Industry Research and Development Institute. Wipe the standard inoculum of the test organism with 10⁵-10⁶ colony-forming units (CFU)/plate onto the surface of the Muller-Hinton (MH) agar plate and place the one impregnated with antimicrobial agent (5 mg/mL) on the agar. The plate was incubated overnight at 37°C and the transparent area around the filter disc was measured to calculate the bacteriostatic ring size. The broth dilution method was used to determine MICs and MBCs, and the antibacterial effect of the composites was evaluated. Tubes containing AgPc-Ormosil/Ag (33 mg) and MH broth (3 mL) were diluted to 0.0011 to 11.0 mg/mL with a 10-fold dilution, and each tube was inoculated with 3.1 × 10⁵ CFU/mL bacteria. The tubes after inoculation of the bacteria are incubated at 37°C for 24 h and then visually checked for their turbidity. MIC is considered to be the lowest dilution concentration for composites and does not produce visible turbidity [18]. To determine the MBC of the sample, assess the viability of the bacteria in a tube with no visible turbidity. 20 microliters of each from tubes with no visible turbidity and evenly spread on MH agar plates, then incubated at 37°C for 18 hours, and the concentration without bacterial growth was the MBC value18].

The effects of the content and duration of the composite on the antibacterial efficacy of S. aureus were further studied by plate counting method. MH agar plates without AgPc-Ormosil/Ag-10 cultured under the same conditions were used as controls. The test process for different concentrations was as follows: 5–40 mg of AgPc-Ormosil/Ag-10 composite was added to 3 mL of MH broth containing 3.02 × 10⁵ CFU/mL of bacteria. The mixture is incubated at 37°C with shaking aerobic incubation for 24 h; Then remove 20 µL of the suspension and incubate it on MH agar plates, followed by an 18-hour incubation at 37°C and count its colony count. The procedure for different inoculation times was as follows: 30 mg of composite was added to a 3 mL of MH broth containing 3.13 × 10⁵ CFU/mL of bacteria. The mixture was incubated at 37°C under vibration for 0.5–48 h, then 20 µL of the above suspension was removed and incubated on agar plates, and incubated at 37°C for 18 h. Measure the optical density (OD) of the agar plate using a colony meter with a wavelength of 600 nm, converting the OD value into the concentration of S. aureus cells. The inhibition zone, MIC, MBCs, and plate counting methods were performed 3 times for each strain, and the results of 2 or more times were used as the results of the strain, and their average values were taken.

3.1 Synthesis and characterization

Solid-state ¹³C and ²⁹Si NMR, XRD, SEM and XPS provided evidence of the formation and structure of AgPc, Pc-Ormosil and the AgPc-Ormosil/Ag composites. ¹³C and ²⁹Si CP-MAS NMR spectra were obtained for the AgPc-Ormosil/Ag composites, as shown in Fig. 2. ¹³C NMR peaks were observed for AgPc-Ormosil/Ag-10 at 10.6 (C-1), 20.8 (C-2), 36.5 (C-3), 45.9 (C-6 and C-7) and 50.5 ppm (C-4 and C-5), which corresponded to the characteristic peaks of [Si–(CH₂)₃NH(CH₂)₂NH(CH₂)₂NH] groups on Ormosil. In addition, the peaks at 141.4 (C-8 and C-9), 125.4 (C-10 and C-11), 133.1 (C-12 and C-13), 151.2 (C-14 and C-15) and 168.5 ppm (C-16 and C-17) corresponded to the characteristic peaks of AgPc– functional groups of AgPc-Ormosil. The ¹³C NMR peaks of the Pc-Ormosil composite partially overlapped (C-3, C-4,5 and C-6,7), and the chemical shift (δ) was weakened by the incorporation of AgNPs (40.1 shift to 36.5 ppm and 48.7 shift to 45.9 ppm). This result was due to dipolar interactions between ¹³C nuclei and the paramagnetic Ag, which provided efficient NMR relaxation sinks [8]. This result was very important because it proves that AgNPs formation on the amine groups of aminosilane, which produced chelation or adsorption on the surface of aminosilane (CH₂NH…Ag). Also, the peaks of AgPc-Ormosil/Ag were of mixed AgPc and Pc-Ormosil functional groups, and that at 151.2 ppm (C-14 and C-15) corresponded to the characteristic peaks of N–Ag–N functional groups on AgPc. The ²⁹Si NMR peaks of the Ormosil network units were observed at − 57.8 (T²), − 68.1 (T³), − 90.0 (Q²), − 101.3 (Q³) and − 110.8 (Q⁴) ppm. T², T³, Q², Q³ and Q⁴ denote R–Si(OSi)₂(OH), R–Si(OSi)₃, Si(OSi)₂(OH)₂, Si(OSi)₃(OH) and Si(OSi)₄, respectively. The structural characterizations of the AgPc-Ormosil/Ag composites were in agreement with the Pc-Ormosil composite expected in light of the ²⁹Si NMR spectra. However, the intensity ratios of Q⁴/Q³ and T³/T² of the AgPc-Ormosil/Ag-10 composite (Q⁴/Q³ = 2.12; T³/T² = 8.48) were larger than those of Pc-Ormosil (Q⁴/Q³ = 1.84; T³/T² = 4.51). These results indicated that the AgNPs were coordinated with silica network units (Si–OH…Ag) at Q³ and T², and the intensity ratios of Q⁴ and T³ were therefore enhanced [8].

Figure 3 shows the XRD diffraction peaks of AgPc, Pc-Ormosil and the AgPc-Ormosil/Ag composites. The peaks obtained for AgPc showed the presence of a sharp and well-resolved diffraction peak, which confirmed its crystalline behavior. The diffraction peaks at 2θ values of 27.9°, 29.6° and 32.3° were due to the crystalline phases of Pc. The 2θ values at 38.1°, 44.2°, 64.4° and 77.3° were indexed as the (111), (200), (220) and (311) faces, respectively, which was consistent with the bulk face-centered cubic Ag single crystal. Observations revealed that the diffraction peak with a d value of 2.37 Å corresponding to a 38.1° angle (2θ) was more prominent. The peak has been indexed in terms of the tetragonal AgPc lattice [19], which indicated that the AgPc-Ormosil/Ag composites contained Ag and AgPc simultaneously.

3.2 Morphology and structure characterization

SEM images were obtained to evaluate the surface morphology and size distribution of the AgNPs deposited in AgPc and AgPc-Ormosil/Ag. The SEM image of AgPc showed the formation of long nanowires, and the lengths of these nanostructures were measured to be 80–300 nm (Fig. 4a). SEM images of the Pc-Ormosil composites show uniform morphology, with the condensation reaction between the Ormosil chains and the Pc crystals forming a cross-linked polymerization (Fig. 4b). The AgPc-Ormosil/Ag composites consisted of non-agglomerated, uniformly distributed AgNPs in the Pc and Ormosil matrix (Fig. 4c and d). The AgNPs in the AgPc-Ormosil/Ag-2.5 composite is mainly concentrated in the Pc matrix, forming spherical AgPc that are uniformly distributed in the Ormosil structure and are in the range of 100–300 nm in size (Fig. 4c). SEM analysis also confirmed that the spherical AgPc and AgNPs were uniformly distributed in the Ormosil structure to form the AgPc-Ormosil/Ag-10 composite, and significantly showed that the spherical AgPc size increases to 200–500 nm (Fig. 4d). The differences of Ag particles in the SEM images of AgPc-Ormosil/Ag-2.5 and AgPc-Ormosil/Ag-10 composites were compared. It was found that according to the content of AgNO₃ in Pc-Ormosil composites, AgNPs preferentially reacted with Pc to form AgPc-Ormosil composite, and more AgNO₃ content reacted with Pc-Ormosil to form AgPc-Ormosil/Ag composite. AgNPs are evenly distributed in the Pc and Ormosil matrices. This behavior could be attributed to the actions of N–Ag–N of Pc and –CH₂NH…Ag of Ormosil as a surface modifier that inhibits Ag particle growth and prevents aggregation.

XPS studies performed on Pc or Ormosil previously loaded with Ag⁺ ions indicated that the complexing main sites were the amines and the secondary alcohol functional groups, as the N atom-pyrrole, –NH–, –NH₂ and –OH groups have a pair of electrons that can add themselves to a cation by a coordinated covalent bond or chemical affinity [19, 20]. The attraction of the electron pair by the atom nucleus is stronger in oxygen, but nitrogen has a greater tendency to donate its pair of electrons to a metal ion to form a complex through a coordinated covalent bond. Figure 5 shows typical XPS spectra of AgPc, Pc-Ormosil and the AgPc-Ormosil/Ag composites. Before Ag induction, for Pc-Ormosil, there were two peaks in the N1s spectra at binding energies (BEs) of approximately 398.1 (N2) and 400.0 eV (N3). These peaks were attributed to the N atoms in the Pc and –NH– groups of Ormosil, respectively. For AgPc, there were two peaks in the N1s spectra at BEs of approximately 398.9 (N1) and 398.1 eV (N2). It is worth noting that a AgPc molecule has two inequivalent nitrogen sites: 2 nitrogen atoms (N1) are connected to the central Ag atom to form a complex bond, while the other 6 nitrogen atoms are linked to iminic carbon (N2; –C = N–C–).

After Ag induction, for AgPc-Ormosil/Ag-2.5, the N1s spectra showed a broad feature, which was fitted to three peaks at BEs of approximately 398.9 (N1), 398.1 (N2) and 400.0 eV (N3). When the Ag amount increased, for AgPc-Ormosil/Ag-10, there were two peaks assigned to N1 and N2 species, and a disappearance in the N3 peak was observed compared with AgPc-Ormosil/Ag-2.5. This result indicated that Ag interacted with the –NH– groups of the Ormosil to form an Ag…NH– complex (similar N1 species). Therefore, the N3 peak disappeared, and the N1 peak intensity increased for AgPc-Ormosil/Ag-10. In the case of AgPc-Ormosil/Ag-2.5, the N1s spectra consisted of the N1, N2 and N3 species. Most likely, the small amount of Ag atoms more strongly reacts with these pyrrolic N atoms (–NH–) in Pc, which is connected with a stronger charge transfer.

The XPS signal for the Ag3d spectra of the AgPc composite consisted of two peaks at 374.7 and 368.8 eV, which were associated with Ag3d_3/2 and Ag3d_5/2 BEs, respectively. For the AgPc-Ormosil/Ag-2.5 composite, the corresponding Ag3d sites were similar to those in AgPc (Ag1 species). This result indicated that AgNPs preferentially react with Pc from AgPc. With an increasing Ag amount, AgPc-Ormosil/Ag-5 and AgPc-Ormosil/Ag-10, the Ag3d_5/2 main peak is broader than that for AgPc and AgPc-Ormosil/Ag-2.5. In the case of the present data of AgPc-Ormosil/Ag-10, we analyzed the peak of Ag3d_5/2 by three components: Ag1 species at 368.8 eV, Ag2 species at 368.2 eV and Ag3 species at 367.1 eV. These peaks were attributed to the Ag atoms interacting with Pc (Ag1), Ag interacting with the –NH– groups of the Ormosil Ag…NH– complex (Ag2) and free Ag atoms in Ormosil (Ag3). These results confirmed that N1s and Ag3d XPS have the same resolution as SEM.

3.3 Antibacterial effects

Inductively coupled plasma‒optical emission spectrometry (ICP‒OES) was used to measure the absorption intensity of a specific silver ion concentration, and a calibration curve was obtained by plotting the intensity of the absorption line as a function of the silver ion concentration of the corresponding standard solution (Fig. 6 insert), which was then used to quantitatively estimate the silver ion release from various samples. Figure 6 shows the Ag⁺ release concentration vs. time of the AgPc-Ormosil/Ag composites (5.0 mg) in 1 L of nitric acid in aqueous solution. At the initial time, the Ag⁺ release concentration increased significantly, the Ag⁺ release began to decrease at 48–60 h, and the release increased with the increase of the AgNPs content in the sample. Since AgNPs are finer and more uniformly dispersed (morphologically) in the composites, possibly due to reduced agglomeration, the water molecules entering the sample interact with more of the AgNPs surface, allowing AgPc-Ormosil/Ag-10 to release more Ag⁺ ions.

The antimicrobial effects of Pc-Ormosil and AgPc-Ormosil/Ag composites against Gram-bacteria were measured by inhibition zone test, MIC, MBC and plate-counting method. Figure 7 and Table 1 detail the bacterial inhibition and antimicrobial ring size of the composites. After 24 h of incubation, the inhibitory region (12.96–19.28 mm) of AgPc-Ormosil/Ag composite was significantly greater than that of Pc-Ormosil (10.66–14.55 mm), and the antibacterial performance was greatly improved by increasing the Ag content of the composite. AgPc-Ormosil/Ag composites exhibited significant inhibitory effects on Gram-bacteria, especially Staphylococcus aureus and Pseudomonas aeruginosa. The MIC and MBC values of the composites against Gram-bacteria are shown in Table 2. The MIC/MBC values of Pc-Ormosil, AgPc-Ormosil/Ag-2.5, AgPc-Ormosil/Ag-5 and AgPc-Ormosil/Ag-10 against bacteria were 11.0/>11.0, 1.10/1.10, 0.11/0.11 and 0.011/0.011, respectively, indicating that the ability of composites to inhibit bacterial growth was in the order AgPc-Ormosil/Ag-10 > AgPc-Ormosil/Ag-5 > AgPc-Ormosil/Ag-2.5 > Pc-Ormosil. AgNPs are closely related to antimicrobial ability, which depends on the AgNPs content in Pc-Ormosil. Compared with the results of our previous literature [7, 8, 22], the AgPc-Ormosil/Ag composites exhibit better antimicrobial properties than Ormosil(NR₄⁺Cl⁻)/Ag, Ormosil/POM, and Ormosil(NR₄⁺Cl⁻)/POM. These results may be due to the relatively small and uniform distribution of AgNPs in the AgPc-Ormosil/Ag composites. Pc-Ormosil samples also showed certain antimicrobial properties, which were attributed to the antimicrobial efficacy of the amine groups in Ormosil and the photosensitizing ability of Pc [8, 14].

Table 1

Zone of inhibition (mm) against bacteria of the Pc-Ormosil and the AgPc-Ormosil/Ag composites.
Bacteria	S. aureus	B. subtilis	P. aeruginosa	E. coli
Blank	0	0	0	0
Pc-Ormosil	12.39	14.55	12.90	10.66
AgPc-Ormosil/Ag-2.5	16.39	15.06	16.56	12.96
AgPc-Ormosil/Ag-5	18.22	16.44	17.78	14.26
AgPc-Ormosil/Ag-10	19.28	17.56	18.38	16.58

Table 2 The MIC and MBC values of the Pc-Ormosil and the AgPc-Ormosil/Ag composites

on bacteria.

Bacteria	S. aureus	B. subtilis	P. aeruginosa	E. coli
	Minimum inhibitory concentration (mg/mL)
Pc-Ormosil	11.0	11.0	11.0	11.0
AgPc-Ormosil/Ag-2.5	1.10	1.10	1.10	1.10
AgPc-Ormosil/Ag-5	0.11	0.11	0.11	0.11
AgPc-Ormosil/Ag-10	0.011	0.011	0.011	0.011
	Minimum bactericidal concentration (mg/mL)
Pc-Ormosil	> 11.0	> 11.0	> 11.0	> 11.0
AgPc-Ormosil/Ag-2.5	1.10	1.10	1.10	1.10
AgPc-Ormosil/Ag-5	0.11	0.11	0.11	0.11
AgPc-Ormosil/Ag-10	0.011	0.011	0.011	0.011

Figure 8 shows the number of bacterial colonies grown on the MH plate as a function of the amount of AgPc-Ormosil/Ag-10 composite and the time of inoculation, when approximately 3.02–3.13×10⁵ CFU/mL S. aureus are applied to the plate. Bacterial colonies grown on plates containing more than 10 mg of AgPc-Ormosil/Ag-10 particles were significantly reduced, and gram-positive S. aureus bacterial colonies were completely killed when treated with 40 mg of AgPc-Ormosil/Ag-10. In addition, bacterial growth was monitored in MH medium supplemented with 3.02–3.13×10⁵ CFU/mL S. aureus cells and 11 mg/mL AgPc-Ormosil/Ag-10 at different inoculation durations. Figure 8b shows that the gram-positive S. aureus bacterial colonies were completely killed 8 h after inoculation, with a 100% reduction rate of bacteria after 8–48 h of inoculation. As the high CFU levels applied in this study are rarely found in real-life systems, it appears that these AgPc-Ormosil/Ag composites could possess an excellent biocidal effect and are effective in reducing bacterial growth, possibly due to the uniform and fine distribution of AgNPs on the surface of Pc-Ormosil. The mechanism of action of Ag⁺ inhibition in bacteria may be that DNA loses its ability to replicate and cellular proteins lose their activity after Ag + action [23]. In addition, studies have shown that Ag⁺, catalyzed by neo-oxygen catalytic oxidation, react with bacterial cell membranes, leading to cell death [24]. The high antimicrobial efficiency of these AgPc-Ormosil/Ag composites may be explained by the high density of AgPc groups and long alkyl chains of ATS in Ormosil matrix.

Aminosilane-modified silicate (Ormosil) was successfully used as a new carrier for the immobilization of AgPc/Ag nanoparticles, and the effect of AgPc/Ag loading on the structure and physical properties of Ormosil was studied. NMR, XRD, SEM, and XPS studies showed that AgPc was bonded to the Ormosil matrix, while the AgNPs were uniformly distributed on the Ormosil matrix. Ormosil acts as a surface modifier and stabilizer for AgPc/Ag nanoparticles, inhibiting the growth of Ag particles and preventing aggregation. AgPc-Ormosil/Ag composites have excellent antibacterial ability: The antibacterial properties of AgPc-Ormosil/Ag composites against Gram-negative E. coli and P. aeruginosa, as well as Gram-positive S. aureus and B. subtilis were studied by MIC, MBC and plate counting methods, and the results showed that AgPc-Ormosil/Ag composites showed strong antibacterial activity against these bacteria. The bacteriostatic efficacy of the composites increased with the increase of AgPc/Ag particles, and was greater than that of Ormosil/Ag, Ormosil(NR₄⁺Cl⁻)/Ag, Ormosil/POM and Ormosil(NR₄⁺Cl⁻)/POM composites. Therefore, AgPc-Ormosil/Ag composites are considered to have great potential as protective materials for biologics.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author Contribution

Kuo-Hui Wu: (1) the conception and design of the study, (2) drafting the article, (3) final approval of the version to be submitted. Wen-Chien Huang, Je-Chuang Wang, Chia-Ling Li and Tsung-Han Yang: synthesis of composites, acquisition of data, analysis and interpretation of data.

Acknowledgement

The authors thank the Ministry Science and Technology for supporting this work (MOST 112-2221-E-606-001).

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Synthesis, characterization and antimicrobial properties of silver phthalocyanine-silver (AgPc-Ag) supported on aminosilane-modified silicate

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Abstract

Figures

1 Introduction

2 Experimental

2.1 Materials and apparatus

2.2 Preparation of AgPc and AgPc-Ormosil/Ag composites

2.3 Test of antibacterial properties

3 Results and discussion

3.1 Synthesis and characterization

3.2 Morphology and structure characterization

3.3 Antibacterial effects

4 Conclusions

Declarations

Conflicts of interest

Author Contribution

Acknowledgement

References

Additional Declarations

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