Au@Ag Core@Shell 나노입자 합성, 항균제로 Rumex hymenosepalus 사용

결과 및 토론

특성화

그림 1a는 합성된 나노물질의 UV-vis 흡수 스펙트럼을 보여줍니다. 흡광도는 각 나노 입자 시스템에 해당하는 최대 국소 표면 플라즈몬 공명(LSPR)에 대해 정규화되었습니다.

나노입자 UV-Vis 스펙트럼(a ), Z-전위(b ), DLS(c ) 및 PDI(d ) Au, Ag 및 Au@AgNPs

그림 1a의 Au@AgNps 흡수 스펙트럼은 AgNPs LSPR(445nm)과 AuNPs LSPR(544nm) 사이에 위치한 474nm를 중심으로 단일 밴드를 가지고 있습니다. Au@AgNPs에 금과 같은 흡수 피크가 없다는 것은 순차적 합성에 의해 얻은 나노물질이 core@shell 구조임을 시사합니다. Au와 관련된 어떤 흡수 밴드도 핵에 속하는 것을 감지할 수 없습니다. 일부 저자는 core@shell 시스템의 경우 흡수 스펙트럼이 3~4nm의 쉘 두께에 대한 각 금속과 관련된 두 개의 밴드로 구성되어 있다고 가정합니다. 금속 코어와 관련된 흡수는 더 높은 두께에서 사라지고 최대 위치가 바이메탈 입자의 두께/코어 크기 비율에 따라 달라지는 단일 흡수 밴드를 얻습니다[79, 80].

Samal et al. [81] 핵 크기를 제어하고 다른 두께의 쉘을 추가하여 core@shell 나노입자(Au@Ag)를 합성했습니다. 특히 Au@AgNPs에 대한 UV-vis 결과는 Samal et al.에 의해 보고된 것과 일치합니다. 스펙트럼이 단일 흡수 밴드(~ 450nm)를 특징으로 하는 32nm 금 코어와 15nm 이상의 은 두께에 대해 Au 표면 플라즈몬의 억제가 관찰됩니다.

또한, 그림 1a에서 Rumex hymenosepalus의 분자에 해당하는 280nm 중심의 흡수(파란색으로 강조 표시된 영역)를 관찰할 수 있습니다. 나노 입자 합성에서 환원제로 사용되는 추출물. 추가 파일 1:그림 S1은 Rumex hymenosepalus에 해당합니다. 수용액 흡수 스펙트럼. 폴리페놀 화합물의 카르보닐 그룹과 결합된 방향족 고리의 전자 전이와 관련된 278nm 중심의 특성 밴드가 관찰됩니다[82]. 나노입자 UV-Vis 스펙트럼의 이러한 흡수 밴드는 최종 제품에 남아 있는 추출물 분자가 포함되어 있음을 나타냅니다(Rivero-Cruz et. 알. 는 R에서 분리된 4개의 stilbenoids, 2개의 flavan-3-ols 및 3개의 anthraquinone을 보고했습니다. 자궁경부 [83] 및 Rodríguez-León et. 알. Rumex hymenosepalus 스틸벤 배당체와 에피카테킨 갈레이트 및 에피갈로카테킨 갈레이트와 같은 중요한 분자를 포함합니다[61]. 이 분자는 나노 입자 합성에서 환원제로 참여합니다. 이 과정은 페놀 고리의 일부 -OH 기의 탈양성자화를 포함하여 =CO 기를 형성합니다. 폴리페놀 분자가 산화되고 방출된 전자가 Ag ⁺ 로 이동합니다. 및 Ag ³⁺ Au ⁰ 을 형성하는 이온 및 Ag ⁰ .

그림 1b는 1, 10, 50, 100µg/mL 농도에서 AuNP, AgNP 및 Au@AgNP에 해당하는 제타 전위 값을 보여줍니다. 나노입자를 초순수에 분산시키고, 25℃에서 3회 반복하여 측정하였다. 일반적으로 농도 범위 전체에서 나노입자는 -30mV보다 음의 제타 전위 값을 나타내며 AuNP 및 Au@AgNP의 경우 100µg/mL 농도 및 AgNP의 경우 -38mV 농도에서 -40mV 값에 도달합니다. 이러한 매우 음의 제타 전위 값은 나노 입자가 응집을 방지하고 금속 콜로이드의 장기간 안정성을 허용하는 반발 상호 작용을 경험함을 나타냅니다[84,85,86]. UV-Vis 분광법 결과를 얻은 제타 전위 값과 상호 연관시킴으로써 우리는 매우 음의 값이 추출물의 폴리페놀 분자가 나노 입자 표면에 착화되어 있기 때문일 수 있음을 확립할 수 있습니다[87].

생물학적 응용의 경우 단분산 크기의 나노입자 집단을 얻는 것이 중요하므로 [88] 그림 1c와 d는 AuNP, AgNP 및 Au@AgNP의 평균 직경 및 다분산 지수(PDI)에 해당하는 DLS 값 1, 10, 50, 100µg/mL Au@AgNPs의 평균 직경은 약 250nm이며 농도의 함수로 일정하게 유지되며, AuNPs 및 AgNPs의 평균 직경이 각각 약 122 및 135nm인 단금속 나노입자의 경우와 유사한 방식입니다. 같은 경우에 PDI 값은 단금속 나노입자의 경우 약 0.3이고 Au@AgNP의 경우 0.2입니다. 농도에 따라 크기가 달라지지 않는 이러한 결과는 다양한 나노입자 시스템이 크기의 중간 정도의 다분산성을 나타내는 양호한 안정성을 가지고 있음을 나타냅니다(0.3 ≥ PDI ≥ 0.2).

Tauc 플롯의 광학 밴드 갭이 계산되었습니다(추가 파일 1:그림 S2). 반도체 재료에 의한 전도대는 E 값을 가집니다. _g <3 eV, 기준 게르마늄은 E _g <0.7 eV 및 실리콘은 E입니다. _g =1.1eV[89]. 우리의 경우 Au@AgNPs, AuNPs 및 AgNPs의 밴드 갭은 각각 1.93eV, 2.03eV, 2.33eV입니다. 이는 이러한 물질이 반도체와 같은 것으로 간주된다는 것을 의미하며, 이러한 특성은 에너지 갭을 증가시키는 양자 구속 효과에 대해 얻어졌기 때문에 나노 물질은 센서, 배터리 및 광전자 소자로 사용될 수 있습니다[64].

유기 화합물이 나노 입자에 존재하는지 확인하기 위해 이러한 나노 물질은 XPS 및 FTIR로 특성화되었습니다. 그림 2a는 식물 추출물과 나노 입자의 조사 스펙트럼을 보여줍니다. 알 수 있는 바와 같이, 모든 나노입자 시스템은 Rumex hymenosepalus의 탄소(C 1 s, 284.6 eV) 및 산소(O 1 s, 532.2 eV) 요소와 관련된 특성 신호를 나타냅니다. 발췌. 이 결과는 추출물에서 추출한 유기 분자가 얻은 나노 물질에 존재함을 확인시켜줍니다. 또한 고해상도 XPS 스펙트럼을 획득하여 나노 입자에서 은과 금의 산화 상태를 분석했습니다(추가 파일 1:그림 S3). AgNP(추가 파일 1:그림 S3A)의 경우 3d3/2 및 3d5/2 스펙트럼 라인에 해당하는 373.76eV 및 367.76eV(∆BE =6.0eV)의 결합 에너지에서의 신호는 Ag ^{0과 연관될 수 있습니다.} (메탈릭 실버). AuNP(추가 파일 1:그림 S3B)의 경우 4f5/2 스핀-궤도 커플링과 관련된 피크는 결합 에너지 87.65eV에 있습니다. 4f7/2의 경우 스핀-궤도 커플링 피크는 83.98eV에 있습니다. 강도(I4f7/2> I4f5/2)의 비율, 위치 및 피크 간 분리(ΔBE =3.67 eV)는 금 이온(Au ³⁺ ) 금속성 금 Au ⁰ 으로 완전히 감소됩니다. [90]. Au@AgNPs의 경우 은과 금에 해당하는 고해상도 XPS 스펙트럼이 각각 추가 파일 1:그림 S3C 및 그림 S3-D에 나와 있습니다. 이 스펙트럼은 단금속 대응물과 동일한 동작을 보여줍니다. 이는 core@shell 프레젠테이션에서 은과 금이 모두 0가임을 나타냅니다.

XPS 조사 스펙트럼(a ) 및 FTIR(b ) Rh, Ag, Au 및 Au@AgNP의 경우

그림 2e의 FTIR은 3296cm ⁻¹ 에서 보여줍니다. 수산기, 2974cm ⁻¹ (C–H) 방향족 고리의 결합, 1689cm ⁻¹ 카르보닐기 스트레칭(C=O) 및 1689–1400cm ⁻¹ 와 관련됨 카르복실레이트 결합(C-O) 및 탄소-탄소 결합 스트레칭 및 1212cm ⁻¹ 로 인해 1049cm ⁻¹ AuNP와 결합된 페놀 CO 스트레칭과 관련됨 카테킨 에스테르 그룹 분자의 CO 스트레치 모드 [88,89,90] 및 799cm ⁻¹ 페놀의 평면 바깥쪽 굽힘, 964.4 및 829.39cm에서 보고된 C–H 굽힘 ⁻¹ 레스베라트롤[91]의 특징이 Rh 추출물에서 1031 및 867 cm로 이동됨 ⁻¹ , 각각 및 AuNPs, AgNPs 및 Au@AgNPs도 이동되어 Rh 추출물의 폴리페놀 분자와 나노 입자의 복합체를 나타냅니다.

Figure 3a corresponds to a representative bright-field STEM micrograph of the Au@AgNPs system at low magnification (100 nm scale bar). A set of nanoparticles without agglomeration and with mostly quasi-spherical geometry can be seen. The same region is shown in dark field (HAADF) in Fig. 3b, and the core@shell structure can be observed, where can we distinguish Au-core looks more intense than Ag-shell, due to the difference in atomic number. Figure 3c and d corresponds to STEM higher magnification micrograph (scale bare 20 nm) of a nanoparticles group of system core@shell in a bright and dark field, respectively. Can be appreciated with clarity brilliant Au core and Ag shell lightly contrasted. These images show that the thickness of the Ag-shell varies between 3 and 5 nm. Additional file 1:Figure S4 corresponds to an individual images gallery where can be observed uniformity of Ag-shell.

Scanning Transmission Electron Microscopy at low magnification (scale bar 100 nm) of Au@AgNPs in Bright Field (a ) and HAADF (b ). A Small group of Au@AgNPs at higher magnification (scale bar 20 nm) in Bright Field (c ) and HAADF (d )

Figure 4a, c, and e corresponds to micrograph TEM of representative nanoparticles systems AuNPs, AgNPs, and Au@AgNPs, respectively. In all cases, nanoparticles have sphere-like morphology and are shown well separated from each other. This can be explained by the extract molecules onto nanoparticle surfaces, acting as spacers between them. Figure 4b, d, and f shows histograms corresponding to size distribution obtained by TEM and performed with 500 nanoparticles collected from 15 to 20 micrographs for each nanomaterial. The histogram presents Gaussian distribution with a mean size of 24 ± 4 nm (AuNPs), 13 ± 3 nm (AgNPs), and 36 ± 11 nm (Au@AgNPs). The discrepancy in values between DLS and TEM measurements with size distribution graph is due to conditions micro-environmental around the nanoparticles, while DLS shows a diameter for a system that includes metal, hydrated coating, and solvent by comparison in TEM measurements is a dry system where measurement is over metal only, in particular, in DLS the molecules used for complexation of nanoparticles (reducing agents and stabilizers) are dispersants that induce errors in sizing measurement and shifts it results to higher values [91].

TEM and size distribution of AuNPs in (a ) 및 (b ), AgNPs in (c ) 및 (d ), and Au@AgNPs in (e ) 및 (f )

Figure 5 corresponds to the Au@AgNPs HAADF-STEM micrographics. A single nanoparticle is shown in Fig. 5a with a gold nucleus and silver cover perfectly delimited, the atomic number (Z) changes through the interface Au@Ag, intensity variations can be quantified by HAADF-STEM [67].

Au@AgNPs HRTEM (a ). Magnification from (a ) of interface core–shell (b ). FFT plot with Miller index (c ) and integrated image from FFT (Inverse) with interplanar distance (d )

The red square region is amplified to obtain an HRTEM micrography of the shell portion (Fig. 5b), and then to verify the crystalline shell structure, the nanoparticle periphery region was analyzed (discontinued square) with the Digital Micrograph 3.0 software (Gatan). Fast Fourier Transform (FFT) image of the selected area was obtained (Fig. 5c). Using the Inverse Fast Fourier Transform was possible to estimate interplanar distances of 2.3 Å, 2.0 Å, and 1.4 Å in Fig. 5d. These distances can be assigned, respectively, to the crystalline planes (111), (200), and (220) of face-centered cubic (fcc) silver according to Inorganic Crystal Structure Database (ICSD) at the FIZ Karlsruhe–Leibniz Institute for Information Infrastructure, Germany or the electron crystallography software Jems (V 4-5430, JEMS-SAAS, Switzerland) [92]. A similar analysis of crystal structure by HRTEM was carried out for monometallic nanoparticles as illustrated in Additional file 1:Figures S5 (for AuNPs) and S6 (AgNPs). In both cases, crystal structure corresponds to face-centered cubic (fcc).

EDS chemical analysis shows the presence of both metals for a group of bimetallic Au@AgNPs observed by TEM (Fig. 6a) in proportions of the atomic weight percent 77% of Ag (shell) and 23% of Au (cores) (Fig. 6b). In comparison, a single bimetallic (Fig. 6c) Au@AgNPs has proportions around 80% of Ag (shell) and 20% of Au (core) (Fig. 6d). To estimate the gold and silver atomic percentage on core@shell nanoparticles (Au@Ag), a quasi-spherical geometry approximation of nanoparticles morphology was considered. The AuNPs average diameter obtained from TEM size distribution (\(\overline{D}_{{{\text{Au}}}} =24\;{\text{nm}}\)) was used for core volume estimation (V _금 ), and Au@AgNPs average diameter \(\left( {\overline{D}_{{{\text{Au}}@{\text{Ag}}}} =36\,{\text{nm}}} \right)\) for core@shell volume estimation \((V_{{{\text{Au}}@{\text{Ag}}}} )\). So, shell volume is determined as \(V_{{{\text{Ag}}}} =V_{{{\text{Au}}@{\text{Ag}}}} - V_{{{\text{Au}}}}\). Total atomic content of Au and Ag was calculated considering an fcc crystalline structure (4 atoms per unit cell) for booth metals where the Au and Ag lattice parameters are 4.0783 Å and 4.0862 Å, respectively [93]. Atomic content estimation by this procedure is 70% for Ag (Shell) and 30% Au (Core), which differs by 10% concerning the measurement obtained by EDS. Figure 7 shows a theoretical estimation of silver and gold content and how varies as the thickness of the shell increases and the size of the core is kept constant (\(\overline{D}_{{{\text{Au}}}} =24\;{\text{nm}}\)). It is observed that for Au@AgNPs with a diameter greater than 30.2 nm, the atomic content of silver exceeds the content of gold. In Supplementary Material, a detailed description of calculation is carried out to obtain atomic contents percentage. Similar estimations of atomic percentages were carried out considering other Au-core diameters and varying Au@AgNPs diameter (Additional file 1:Figure S7A-B).

TEM and EDS of an Au@AgNPs group (a , b ) with Au 23 and Ag 77% at. and single Au@AgNPs (c , d ) with Au 20 and Ag 80% at

Variations of atomic content percentage versus increase thickness shell, where diameter AuNPs (24 nm) was kept constant

Figure 8 corresponds to XRD patterns for AuNPs and AgNPs as well as bimetallic Au@AgNPs. All the synthesized products have fcc crystalline structure as previously reported in the characterization by electron microscopy. Peaks for Au@AgNPs are located at 2θ diffraction angles of 38.25°, 44.4°, 64.9°, 77.85°, and 81.25°. As can be appreciated in the figure, the AgNPs and AuNPs diffraction peaks are found in the same positions mentioned with a difference of ± 0.5°. This is because Au and Ag have very similar lattice constants, so their diffraction patterns for fcc crystal structure are almost identical [94,95,96]. In this way, the diffraction peaks in Fig. 8 are assigned, respectively, to the crystalline planes (111), (200), (220), (311), and (222) of the gold and silver fcc structure by JCPDS:4-0783 and 4-0784 [97].

X-ray Diffraction AuNPs (pink), AgNPs (brown), and Au@AgNPs (red)

Antimicrobial Activity

Monometallic (AgNPs, AuNPs) and bimetallic (Au@AgNPs) materials were tested at four different concentrations:1, 10, 50, and 100 μg/mL. Selected microorganisms to evaluate antimicrobial activity were yeast Candida albicans , Gram-positive bacteria S.aureus , and Gram-negative bacteria E. 대장균 . Growth kinetics curves in a time-lapse of 24 h are shown in Fig. 9.

The growth curves using AuNPs, AgNPs, and Au@AgNPs like inhibitory treatments on Candida albicans (아 –ㄷ ), Escherichia coli (d –f ), and Staphylococcus aureus (지 –나 )

Candida albicans

AuNPs show no effect on growth kinetics until 10 h (Fig. 9a), varying in a dose-dependent manner the absorbance reached at 24 h. Interestingly, with 50 µg/mL or more, the growth kinetic shows a steep negative slope from 10 h until reaching a 45% reduction at 24 h, which suggests an antifungal effect of these materials. This can be attributed to the ability of gold nanoparticles to interact with relevant proteins present in fungus such as H ⁺ -ATPase, affecting proton pump activity. This atrophying the ability of yeast to incorporate nutrients causing its death [61]. In Fig. 9b and c was observed that AgNPs and Au@AgNPs inhibit the growth of the yeast Candida albicans from 10 µg/mL. The determination of the MIC₅₀ concentration for both materials was estimated from the dose–response curve shown in Additional file 1:Figure S8. MIC₅₀ is defined as the concentration of nanoparticles that produces a 50% decrease in absorbance concerning the control (yeast without treatment). For AgNPs and Au@AgNPs, MIC₅₀ were 2.21 µg/mL and 2.37 µg/mL, respectively.

However, according to the EDS results (Fig. 9b), the silver content in Au@AgNPs is 64.85% mass. Thus, the concentration of silver in Au@AgNPs for MIC₅₀ is 1.53 µg/mL, 30% lower than in the case of AgNPs. Padmos et. 알. have demonstrated that silver nanoparticles possess important antibacterial features, but are cytotoxic by mammalian cells this effect has reduced using bimetallic nanoparticles especially using gold in the core of bimetallic nanoparticles [35].

Escherichia coli

In Fig. 9d, AuNPs do not show significant inhibition (< 15%) or affect the growth kinetics of E. 대장균 . For AgNPs (Fig. 9e) at low concentrations, the Lag phase remains unchanged, but there is a marked decrease in growth ratio indicated by the slope decrement. At 50 µg/mL Lag phase lasts up to 16 h and viability reaches a maximum of 20% at 24 h. For 100 µg/mL, an apparent detachment of the growth phase of the microorganism is not observed. In Au@AgNPs (Fig. 9f), the first two concentrations do not show changes in their growth phase, but a phase delay of up to 2 h is observed compared to the control. It is interesting to note that the lag phase lasts up to 21 h for the 50 µg/mL concentration, finally there is no explicit growth behavior for the 100 µg/mL concentration.

Staphylococcus aureus

A comparative analysis of lag phase regrowth occurred after 12 h for Au (Fig. 9g), Ag (Fig. 9h), and Au@AgNPs (Fig. 9i) in the case of S. 구균 at 50 µg/mL. For the highest concentration at 100 µg/mL, there is no growth of the bacteria. Additionally, we observe changes in the slope of respect control for Au, Ag, and Au@AgNPs at 1 and 10 µg/mL.

AuNPs interaction with these Gram-positive bacteria could be due to the charged surface that causes an electrostatic interaction, destabilizing membrane structure. Similar results, but with higher NPs concentrations, are reported for AuNPs synthesized using Ananas comosus fruit extract as reducing agent [98] and blue-green alga Spirulina platensis protein [99]. Yang et al. show MIC > 500 µg/mL for S. 구균 (CMCC(B)26003), our AuNPs has shown inhibition with 10 times less concentration; in this case, a critical synergy exists with polyphenols molecules on coating and stabilizing the surface of nanoparticle [100]. ROS is generated of less to higher intensity [101] by AuNPs, polyphenols (plant extracts), and AgNPs, so AuNPs in synergy with resveratrol and epigallocatechin gallate (EGCG) promote antibacterial response over S. 구균 [102] had the most feasible mechanism in this case. Penders et al. reported 250 and 500 µg/mL of AuNPs-like antibacterial agents over S. 구균 increases in bacterial growth lag time and antibacterial effect [61, 98, 99].

We believe that inhibition is caused by AgNPs [103] accumulation and diffusion on bacteria related to NPs surface charges that promote electrostatic interactions [104] with the bacteria's membrane leading to higher penetration and damage. We think this is a similar mechanism described for interactions between E. 대장균 biofilms and AgNps [105].

For Au@AgNPs, the obtained results are comparable to those reported by other workgroups [100, 101]; however, different authors suggest that the inhibition of the growth of the microorganisms is directly related to the thickness of the shell [100, 101]. Core–shell NPs showed low cytotoxicity when tested in NIH-3T3 fibroblasts cells (normal mammalian cells) [35]. A lower proportion of silver in the shell of the Au@AgNPs shows similar results to AgNPs [100], and Au core potentializes antibacterial effect, and minimizes the cytotoxicity.

Curves Growth Analyzed by the Modified Gompertz Model

To know how the growth ratios (µ ) and Lag phase (λ ) are quantitatively modified, the growth curves of microorganisms exposed to different concentrations of nanomaterials (Fig. 10) were adjusted by the Gompertz model (Eq. 2).

Kinetic parameters were obtained by the Gompertz model. Growth Rate µ and Time Lag Phase \(\lambda\) for S. 구균 (아 , b ) and E. 대장균 (ㄷ , d )

In Fig. 10a, it can be seen that all nanomaterials produce a decrease in the replication rate of S. 구균 populations when the concentration of nanoparticles increases. This effect results in slightly higher sensitivity for AuNPs. At a concentration of 50 µg/mL, the growth ratio is only 30% concerning control (Additional file 1:Tables S1-S24); at a concentration of 100 µg/mL, all materials inhibit the growth of the S. 구균 인구. The behavior of the adaptive phase for S. 구균 with the different treatments is shown in Fig. 10b. It is observed that there are no significant differences in the material used, and at 50 µg/mL, the Lag phase has increased by almost 5 times compared to the adaptive phase of S. 구균 (Additional file 1:Tables S1-S24). In general, we can establish that the different nanomaterials evaluated in S. 구균 reduce the replication rate and postpone the adaptive phase in a dose-dependent manner until its inhibition at 100 µg/mL.

Figure 10c clearly shows that AuNPs do not affect the growth ratio µ of E. 대장균 bacteria. Meanwhile, AgNPs produce a decrease over µ , reaching a minimum value corresponding to 19% to the control (µ for E.coli without treatment) for 50 µg/mL (see Additional file 1:Table S52). In contrast, Au@AgNPs completely inhibit the E. 대장균 growth at 100 µg/mL. Analysis of the behavior of E. 대장균 Lag phase exposed to different materials is shown in Fig. 10d. In this case, unlike Fig. 10b, each material has a characteristic response. Thus, AuNPs do not generate any modification in the adaptive phase of E. 대장균 , while AgNPs and Au@AgNPs have a dose-dependent effect on the Lag phase, the latter material standing out. Thus, we can establish that AuNPs have no appreciable effect on E. 대장균 bacteria, and Au@AgNPs can inhibit replication and, therefore, indefinitely postpone the Lag phase of E. 대장균 . Interestingly, this effect is not achieved for AgNPs even though the net silver content is higher than in Au@AgNPs. This suggests that the core@shell presentation of both metals produces a synergy that favors antimicrobial activity. Feng et. 알. have reported an electron compensation phenomena from Au to Ag in core–shell and alloy structures, which derive in enhance the cytotoxicity of nanoparticles but kept it the antibacterial properties, that means, a synergy between Au and Ag are assumed, due to observed differences between the monometallic and bimetallic materials [106], but more research is necessary.

Figure 11 shows the results of the direct count study of colonies of microorganisms exposed to nanomaterials. In general, the behavior of the microorganism populations reproduces the results obtained from the growth kinetics study (Fig. 7a, e, i). For example, in Fig. 11a, the population of microorganisms (represented logarithmically) decreases significantly only at 19 h where AuNPs have killed 92% of C. albicans . Interestingly, for nanoparticles containing silver (Fig. 11b, c) a more pronounced population decline is observed. Au@AgNPs system at 50 µg/mL, almost entirely inhibits S. 구균 at 7 h (99.5% of bacteria killed) although microorganism reactivates its growth for later times. MBC determination was not possible to obtain for tested concentrations (Additional file 1:Figure S9-11), according to experimental observation higher concentrations are required to show this effect. However, for C. albicans , AgNPs showed an MBC value of 50 µg/mL (Additional file 1:Table S55).

Effect of nanoparticles over microorganisms growth C. albicans exposed to AuNPs (a ), E. 대장균 exposed to AgNPs (b ), and S. 구균 exposed to Au@AgNPs (c ). All microorganisms were exposed at 50 µg/mL nanoparticles concentration