sign in sign up
<<
Home , Polymer

Journal of and Interface Science 460 (2015) 128–134

Contents lists available at ScienceDirect

Journal of Colloid and Interface Science

journal homepage: www.elsevier.com/locate/jcis

Plasmonic-polymer hybrid hollow microbeads for surface-enhanced Raman scattering (SERS) ultradetection ⇑ Anna Trojanowska a,b, Nicolas Pazos-Perez b,c, Cinta Panisello b, Tania Gumi a, Luca Guerrini b,c, , ⇑ Ramon A. Alvarez-Puebla b,c,d, a Departament d’Enginyeria Química, Escola Tècnica Superior d’Enginyeria Química, Universitat Rovira i Virgili, Av. Països Catalans, 26, 43007 Tarragona, Spain b Centro de Tecnologia Quimica de Cataluña and Universitat Rovira i Virgili, Carrer de Marcellí Domingo s/n, 43007 Tarragona, Spain c Medcom Advance SA, Viladecans Business Park – Edificio Brasil, Bertran i Musitu 83-85, 08840 Viladecans – Barcelona, Spain d ICREA, Passeig Lluís Companys 23, 08010 Barcelona, Spain graphical abstract

article info abstract

Article history: Hybrid composites are known to add functionality to plasmonic . Although these sub- Received 15 July 2015 strates can be produced by common synthetic methods, the percentage of metal loaded into the func- Revised 20 August 2015 tional is usually small. Herein, we exploit a inversion precipitation method to Accepted 22 August 2015 incorporate large amounts of silver inside the polymeric matrix of microbeads. Available online 24 August 2015 The combines the high SERS activity resulting from the plasmonic coupling of highly interacting nanoparticles and the ability to accumulate analytes of the polysulfone porous support. This Keywords: allows for the quantitative SERS detection down to the nanomolar level, with a liner response that Surface-enhanced extends over an impressive concentration range of five orders of magnitude. Plasmonic Ó Metallic nanoparticles 2015 Elsevier Inc. All rights reserved. Hybrid Polysulfone Phase inversion precipitation Hot-spots Analyte accumulation Microbeads Ultradetection

⇑ Corresponding authors at: Centro de Tecnologia Quimica de Cataluña and Universitat Rovira i Virgili, Carrer de Marcellí Domingo s/n, 43007 Tarragona, Spain. E-mail addresses: [email protected] (L. Guerrini), [email protected] (R.A. Alvarez-Puebla). http://dx.doi.org/10.1016/j.jcis.2015.08.047 0021-9797/Ó 2015 Elsevier Inc. All rights reserved. A. Trojanowska et al. / Journal of Colloid and Interface Science 460 (2015) 128–134 129

1. Introduction favoring the diffusion of the analyte through the support and its positioning close/onto the plasmonic surfaces. Surface-enhanced Raman spectroscopy (SERS) is an ultrasensi- Herein, we present a novel synthetic strategy for the incorpora- tive technique for the identification of a variety of analytes [1–4]. tion of silver nanoparticles (AgNPs) in high content within the However, since its initial discovery [5], this technique has been lar- polysulfone microbeads (PSf) of high porosity, based on the phase gely limited to qualitative and semi-quantitative applications due inversion precipitation method. As a result, these composite mate- to the intrinsic inhomogeneities derived from the fabrication of rials (PSf/Ag) accommodate a densely packed collection of efficient active plasmonic materials, as well as from their largely variable hot spots while providing large accessibility for the target mole- and molecular-specific binding affinity for different analytes. In cules to the metallic surfaces, allowing for the SERS quantitative the recent years several works described new plasmonic platforms detection in a window of five orders of magnitude. with the ability of reporting quantitative results. These studies are mainly based in lithographic techniques including physical evapo- 2. Experimental ration with electron or ion beam patterning, nanosphere lithogra- phy or direct imprinting of plasmonic colloidal particles [6]. 2.1. Materials Despite their good performances, these methods require expensive setups for fabrication, and cannot be easily industrialized. Addi- Trisodium citrate, silver nitrate (99.9%, AgNO3), tionally, linearity in their optical response is limited to no more (PVP, Mw = 40,000), N,N-Dimetilformamida than two orders of magnitude [7,8]. (DMF), ethanol (EtOH), and Polysulfone (PSf, Mw = 16,000) were To address such issues, colloidal fabrication of plasmonic sub- purchased from Sigma Aldrich. All reactants were used without strates for SERS has evolved in different directions, such as the further purification. Milli-Q water was used in all aqueous combination of metallic nanoparticles with non plasmonic materi- . als acting as support or matrix. The principal goals of constructing these composite materials include the formation of stable hot 2.2. Synthesis of silver nanoparticles spots, the increase in size of the plasmonic platform up to the micrometer scale in order to make easier their integration into Silver nanoparticles (AgNPs) of ca. 50 nm diameter were syn- sensing devices; and the development of analyte-trapping capabil- thesized as follows. Briefly, 1 L of milli-Q water was heated under ity to concentrate the target . Materials selected as sup- vigorous stirring. 6.8 mL of an aqueous of trisodium port for plasmonic particles include inorganic , mainly citrate (0.1 M) and 0.996 mL of an aqueous solution of ascorbic acid silica [9] or oxides [10], and polymers such as (0.1 M) were consecutively added to the boiling water. After 1 min, [11]. As a matrix, the preferred materials are usually polymers 0.744 mL of AgNO (0.1 M) were also added to the mixture. The including agarose [12,13], [14], polyallylamine 3 solution was kept boiling for 1 h under stirring and then left to cool [14], [15], poly(N-isopropyl acrylamide-- down to room temperature. AgNPs were functionalized with PVP 2-hydroxyethyl ) [16] or polystyrene [15], using tech- by mixing 1 L of into an aqueous solution of PVP (5 g in niques such as microfluidic flow focusing [12], or suspension [17] 20 mL) to yield polymer-stabilized nanoparticles (AgNPs@PVP). and living [18]. Notably, these fabrication methods The suspension was maintained under continuous stirring during give rise, on the one hand, to dense polymer structures with low 24 h at room temperature. Afterwards, the solution was cen- porosity, thus hampering the analyte diffusion inside the matrix trifuged twice (7000 rpm, 30 min), the supernatant was discarded and, on the other hand, to low amount of trapped nanoparticles and the AgNPs@PVP sediment was redispersed in 1 mL of DMF. (around 1% as compared with the total weight of the material), which severely limits the extensive generation of hot spots (i.e. low SERS activity). Furthermore, the analyte diffusion to the inner 2.3. Microbeads preparation parts of the may be undetected by SERS due to the limited laser penetration across the thick composite structure, Hybrid polysulfone/AgNPs microbeads (PSf/Ag) were prepared leading to an underestimation of the analyte detection. by phase inversion precipitation method [20]. Briefly, a polymeric These disadvantages mainly arise from the fact that most of the solution was prepared by dissolving 15% w/w of PSf in DMF fabrication methods of -polymer composites require (2.490 mL) followed by the addition of the AgNPs@PVP dispersion the mixing of phases where the solubility of the polymers in DMF (1 mL). The final composition of the polymeric solution was is much larger than that of the nanoparticles (i.e. the nanoparticle 82.3% of DMF, 15% of PSf and 2.7% of AgNPs (w/w). The mixture concentration is low). On the other hand, a minimum quantity of was stirred during 24 h at room temperature. To form the microbe- polymer is required to form the polymer matrix, which remains ads, an airbrush device working in semi-continuous process with a much larger than the maximum tolerated nanoparticle concentra- nozzle size of 800 lm was employed [20,21] to produce micro- tion in the mixture. Furthermore, the combination of hydrophilic droplets which precipitate in a coagulation bath containing and hydrophobic solvents as required in some fabrication methods 500 mL of water. Finally, the microbeads were collected by filtra- (i.e. microfluidics or suspension and dispersion polymerization), tion using a 5 lm filter and were stored under vacuum in usually leads to colloidal instability and, thus, uncontrolled a desiccator. nanoparticle aggregation. As an alternative synthetic strategy to circumvent such prob- 2.4. Characterization lems, one can relies on layer-by-layer protocols [14]. However, these methods are extremely time-consuming, especially for the Evolution 201 UV–Visible Spectrophotometer (Thermo fabrication of large batches of discrete microcapsules. On the con- Scientific) with a Hg source and a wavelength range from trary, phase inversion precipitation methods [19] allow to increase 300 to 850 nm was employed to measure the absorption of silver the nanoparticle content by reducing the amount of polymer far colloids. External morphology of PSf/Ag microbeads was analyzed below the minimal concentration required by the common by JEOL JSM 6400 Scanning Microscopy Series, with acceleration methods. Importantly, since the driving force to form the beads voltage of 15–20 kV. Particles size distribution was determined is air, highly porous hollow microparticles can be produced, thus by analyzing the SEM micrographs. Internal morphology of PSf/ 130 A. Trojanowska et al. / Journal of Colloid and Interface Science 460 (2015) 128–134

Fig. 1. Schematic representation of (A) the preparation of polysulfone/ microbeads (Psf/Ag); and (B) their functionalization with the Raman probe for SERS characterization.

Fig. 3. SEM micrographs of PSf/Ag microbeads and the corresponding size histogram.

Fig. 2. (A) Localized surface resonance of silver colloids and the corresponding (B) nanoparticle size distribution (a representative TEM image of inclusion and cryogenic breaking. Both analysis were performed the dried colloids is also included). according to the procedure described by Torras et al. [22]. Thermogravimetric analysis (TGA) was employed to determine Ag microbeads was analyzed via a Quanta 600 FEI Scanning Micro- the inorganic content in PSf/Ag by registering the loss of weight scope with acceleration voltage of 20–30 kV. The wall thickness of of the organic material, associated to the polysulfone degradation the microbeads and their internal diameter were determined by and vaporization, upon temperature increasing. The microbeads ESEM micrographs analysis. samples (about 10 mg) were introduced into an aluminum The content of Ag within the capsules was determined through crucible and analyzed by TGA under controlled temperature and an elemental composition analysis by energy-dispersive X-ray a constant flow of of 290 cm3/min by using a Perkin Elmer spectroscopy (EDS). Internal structural investigation of the model Thermobalance TGA7 device equipped with a microbalance microbeads was performed by cross section analysis of the PSf/ with an accuracy of 1 lg. The samples were heated from 30 to Ag microbeads micrographs through two different methods: 900 °C at a rate of 10 °C/min. A. Trojanowska et al. / Journal of Colloid and Interface Science 460 (2015) 128–134 131

Textural characterization PSf/Ag microbeads was determined microparticles by a Â50 objective (0.75 NA) with accumulation through adsorption-desorption experiments using a Micrometrics times of 10 s. ASAP-2020 device. The analysis was performed with 0.0111 g of The averaged SERS spectra and the spectral marker values (the

PSf/Ag microbeads at 77.3 K. The pore size distribution was calcu- SERS intensity ratio I999/I791) reported in the manuscript were lated from the nitrogen adsorption data using the NLDFT model obtained as follows. First, 10 spectra were acquired on different (Non Localized Density Functional Theory) based on a slit pore PSf/Ag capsules dried on a slide. The resulting spectra were equilibrium model. baseline corrected and normalized to the 791 cmÀ1 PSf band before Surface-Enhanced Raman Scattering (SERS) spectra were col- the corresponding averaged spectrum was calculated. The SERS lected in backscattering geometry with a Renishaw Invia Reflex intensity ratio I999/I791 was acquired from such averaged SERS system equipped with a 2D-CCD detector and a Leica confocal spectra. The same protocol was applied to the Raman characteriza- microscope. Samples for SERS analysis were prepared by adding tion of the pure PSf beads. 10 lL of ethanolic solutions of thiophenol at different concentra- tions from 1 mM to 0.1 lM to 1 mL suspension of dispersed 3. Results and discussion microbeads. Thin films were created by drop-casting 10 lL of these mixtures on glass slides and then analyzed after solvent evapora- Fig. 1 schematically depicts the fabrication process and compo- tion. A 785 nm diode laser was focused onto the dried PSf/Ag sition of our composite material polysulfone/silver nanoparticle microbeads (PSf/Ag). Controlling the geometry of the preformed nanoparticles is a key feature to obtain a homogeneous distribution of hot spots in the hybrid material. Although gold nanoparticles can be prepared almost in every size and shape [23,24], the presence of strongly damped plasmon resonances in gold nanostructures when excited with green or more energetic lasers limits their application as effi- cient SERS materials because of the coupling to interband transi- tions [25,26]. Differently, other plasmonic materials such as

Fig. 4. (A) Representative cross-sectional ESEM image of one microbead prepared by cryogenic break. (B) Textural characterization of Psf/Ag beads by N2 adsorption– desorption isotherm. Low N2 adsorption takes place in the relative pressure P/Po in the range from 0 to 0.8. Above this threshold, adsorption rapidly arises due to the interactions of N2 with previously adsorbed . (C) Pore size distribution Fig. 5. (A) Elemental compositional analysis of PSf/Ag microbeads via energy-

(red line) and cumulative pore volume (blue line) calculated from the N2 dispersive X-ray spectroscopy (EDS). The elemental spectrum clearly shows the adsorption–desorption isotherm using the NLDFT model based on slit pore- presence of Ag (red ) and S (green color) coming from the AgNPs and equilibrium model. The data show pores of different sizes ranging from 2.4 to polysulfone, respectively. (B) Thermogravimetric analysis (TGA) of Psf and PSf/Ag 15.2 nm. (For interpretation of the references to color in this figure legend, the microbeads. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) reader is referred to the web version of this article.) 132 A. Trojanowska et al. / Journal of Colloid and Interface Science 460 (2015) 128–134 silver generate much efficient electromagnetic fields with the Pore size distribution was calculated by using the non-local density subsequent increase in the SERS signal. Unfortunately, silver is functional theory (NLDFT) based on a slit pore equilibrium model more reactive than gold and, thus, homogeneous preparation of [30]. The calculations (Fig. 4C) display an extended fluctuation of nanoparticles becomes difficult, especially as their size increases. the pore size in the range from 2.4 to 15.2 nm, diameters large Thus, for our composite material we selected spheroidal silver enough for small and medium molecules to diffuse into the matrix. particles with a diameter of 50 nm as a compromise in between Composition of the beads was characterized by ESEM–EDS homogeneity and size. Fig. 2 shows a plasmon centered at (energy-dispersive X-ray spectroscopy) and thermogavimetric 402 nm with a narrow nanoparticle size distribution of ca. 48 nm analysis (TGA) (Fig. 5). Notably, the EDS mapping shows a well diameter. As a polymeric ingredient, polysulfone was selected distributed amount of silver into the material while the TGA since it provides a porous matrix with low SERS-cross section indicates contents of metal above 10%, considerably larger than and is soluble in DMF. This latter property is important as our those of similar materials produced by other methods. nanoparticles can be also concentrated in this solvent favouring The SERS performance of PSf/Ag beads was investigated by illu- the loading of metal into the final material. minating the sample with a 785 nm laser and using thiophenol Thus, for the preparation of PSf/Ag both solutions were mixed (TP) as a Raman probe. TP is a molecule with high Raman cross- and atomized using an airbrush to form microdroplets into a water section which strongly binds silver nanostructures providing a bath [20]. Fig. 3 shows SEM images of the resulting PSf/Ag characteristic vibrational fingerprint [31]. PSf/Ag capsules were microbeads and the corresponding histogram which reveals a immersed into TP solutions at increasing analyte concentration mean diameter of 18 lm. The cross-sectional ESEM image of one and the corresponding Raman signals were acquired by focusing bead (Fig. 4A) corroborates its hollow nature. The volume of the the laser onto dried microbeads, deposited over a glass slide, using internal cavity contributes on average to the 18.2% of the whole a Â50 objective. For each sample, at least 10 capsules were inves- bead volume. tigated to yield the corresponding averaged spectra illustrated in A careful examination of the cross section images reveals a pore Fig. 6A. For the sake of comparison, the spectra were also normal- network within the walls of the beads. Thus, the surfaces of the ized to the intensity of the strongest band. In the absence of TP, beads were explored by means of nitrogen (77 K) adsorption only polysulfone features appear in the spectra, such as the À1 À (Fig. 4B). The adsorption–desorption isotherm can be clearly classi- m(C–S–C) mode at 791 cm , the symmetric and asymmetric SO2 fied as a IUPAC type III [27,28], indicating a material with low affin- stretching at 1073 and 1109 cmÀ1, respectively, and the symmetric ity for nitrogen. The surface area, evaluated by applying BET, gave C–O–C stretching at 1148 cmÀ1 [32]. As the TP concentration is rise to 30 m2/g with a total pore volume of 0.064 cm3/g. Notably, progressively increased, the characteristic bands of the molecular the corresponding values for pure PSf capsules are 27 m2/g and probe gradually emerge such as, among others, the intense TP 0.128 cm3/g, respectively [29]. Thus, incorporation of AgNPs within features at 999 and 1022 cmÀ1, both ascribed to in-plane ring the polymer matrix generates a ca. 10% increase of surface area but breathing vibrations, and at 1074 cmÀ1, assigned to an in-plane with a large reduction of the total pore volume. This fact might be ring breathing mode coupled with m(C–S) [33]. As it can be seen, associated with the presence of the nanoparticles inside the pores. TP bands can be clearly distinguished down to the nanomolar

Fig. 6. (A) Normalized averaged SERS spectra (N = 10) of TP on PSf/Ag capsules at different concentrations in the 700–1200 cmÀ1 spectral range and the corresponding. (B) TP concentration dependence of the ratiometric peak intensities I999/I791. (C) Normalized averaged Raman spectra (N = 10) of TP on PSf capsules at different concentrations in the 900–1200 cmÀ1 spectral range and the corresponding. (D) Difference spectra obtained by subtracting the Raman signal of the pure PSf to each PSf + TP spectrum. A. Trojanowska et al. / Journal of Colloid and Interface Science 460 (2015) 128–134 133 regime, with a limit of detection of ca. 1 nM and an estimated toward different goals. For instance, efforts could be devoted to analytical enhancement factor of ca. 4 Â 105 (see Supplementary the improvement of the reported synthetic protocol such as to Information for details about the calculation). It is important to achieve larger nanoparticle loading, better control over bead size that the 785 nm laser was selected as the optimum excita- distribution, tuning of the polymeric porosity for additional size- tion source after comparing the SERS response of the PSf/Ag exclusion selectivity, minimizing the extension of the PVP microbeads for TP 10À5 M upon illumination with three different of the nanoparticles to maximize analyte diffusion toward the lasers (532 nm, 633 nm and 785 nm). The corresponding SERS metallic surfaces, etc. On the other hand, introduction of different efficiencies decrease as follows: 785 nm > 633 nm  532 nm. This metallic nanoparticles with enhanced plasmonic performance result suggests that silver nanoparticles included in the polymeric (i.e. nanorods, nanocubes, nanostars, etc.) may further increase matrix are closely interacting to each other leading to a large red the sensitivity of the sensing platform. shift and broadening of plasmon resonance frequency to longer wavelengths. Acknowledgments To quantitatively monitor the SERS response of PSf/Ag sub- strates as a function of the TP concentration, we selected the PSf This work was funded by the European Research Council À1 feature at 791 cm as an internal standard and, then, calculated (CrossSERS, FP7/2013 329131, PrioSERS FP7/2014 623527), the the corresponding ratiometric peak intensities I999/I791 which is Spanish Ministerio de Economia y Competitividad (CTQ2014- plotted against the Raman probe concentration in Fig. 6B. The 59808R), the Generalitat de Catalunya (2014-SGR-612) and Med- 2 calibration curve shows a very good linear correlation (r > 0.98) com Advance SA. A.T. acknowledges the Departament d’Enginyeria over an impressive 5 orders of magnitude concentration range Química de la URV for funding and Dr. Renata Jastrza˛b (Coordina- (from 1 mM to 10 nM). tion Department, Adam Mickiewicz University, Poznan, As a control experiment, we performed an identical Raman Poland). study on pure PSf capsules (i.e. no AgNPs) exposed to TP solutions at different concentrations (Fig. 6C). As for PSf/Ag measurements, the samples were extensively washed prior to the SERS analysis Appendix A. Supplementary material to remove any unbound TP molecules from the dispersion. In this case, the data indicate that TP does accumulate inside the matrix Supplementary data associated with this article can be found, in yielding a normal Raman signal that can be observed at bulk the online version, at http://dx.doi.org/10.1016/j.jcis.2015.08.047. concentration as low as 0.1 mM. This is well revealed by the differ- ence spectra shown in Fig. 6D, which were obtained by digitally References subtracting the signal of PSf from those of the PSf + TP mixtures. However, the overall spectral intensity remains extremely [1] S. Schlücker, Surface-enhanced Raman spectroscopy: concepts and chemical smaller than that observed in the case of PSf/Ag indicating that applications, Angew. Chem. Int. Edit. 53 (2014) 4756–4795. [2] R.S. Golightly, W.E. Doering, M.J. Natan, Surface-enhanced Raman spectroscopy TP vibrational spectra acquired on PSf/Ag is almost entirely due and homeland security: a perfect match?, ACS Nano 3 (2009) 2859–2869 only to the SERS contribution (i.e. TP molecules attached or in close [3] F. Casadio, M. Leona, J.R. Lombardi, R. Van Duyne, Identification of organic proximity to the metal surface). On the other hand, these findings colorants in fibers, paints, and glazes by surface enhanced Raman spectroscopy, Acc. Chem. Res. 43 (2010) 782–791. also suggest that such ‘‘analyte accumulation” effect promoted by [4] R.A. Alvarez-Puebla, L.M. Liz-Marzan, SERS detection of small inorganic the PSf matrix may be at the root of the remarkable extended linear molecules and ions, Angew. Chem. Int. Ed. 51 (2012) 11214–11223. range of response of the PSf/Ag substrate. In fact, whereas in the [5] M.G. Albrecht, J.A. Creighton, Anomalously intense Raman-spectra of pyridine at a silver electrode, J. Am. Chem. Soc. 99 (1977) 5215–5217. case of AgNPs in suspension the maximum number of detectable [6] H. Ko, S. Singamaneni, V.V. Tsukruk, Nanostructured surfaces and assemblies TP molecules is substantially limited by the surface silver area as SERS media, Small 4 (2008) 1576–1599. available for the binding (i.e. first ), for PSf/Ag [7] M. Sackmann, A. Materny, Surface enhanced Raman scattering (SERS) – a hybrid materials the molecular probe has the possibility to occupy quantitative analytical tool?, J Raman Spectrosc. 37 (2006) 305–310. [8] S. Kasera, L.O. Herrmann, J.d. Barrio, J.J. Baumberg, O.A. Scherman, Quantitative and accumulate in the whole volume surrounding the metal. As a multiplexing with nano-self-assemblies in SERS, Sci. Rep. 4 (2014) (article result, a much larger number of analyte molecules can profit from number: 6785). the electromagnetic enhancement generated by the nanostruc- [9] D. Tsoutsi, J.M. Montenegro, F. Dommershausen, U. Koert, L.M. Liz-Marzán, W.J. Parak, R.A. Alvarez-Puebla, Quantitative surface-enhanced Raman scattering tures upon laser excitation. ultradetection of atomic inorganic ions: the case of chloride, ACS Nano 5 (2011) 7539–7546. [10] J. Lim, S.A. Majetich, Composite magnetic–plasmonic nanoparticles for biomedicine: manipulation and imaging, Nano Today 8 (2013) 98–113. 4. Conclusions [11] R. Ahijado-Guzman, P. Gomez-Puertas, R.A. Alvarez-Puebla, G. Rivas, L.M. Liz- Marzan, Surface-enhanced Raman scattering-based detection of the In summary, we exploited the phase inversion precipitation interactions between the essential cell division FtsZ and bacterial membrane elements, ACS Nano 6 (2012) 7514–7520. method to incorporate large amounts of silver nanoparticles inside [12] S. Abalde-Cela, B. Auguie, M. Fischlechner, W.T.S. Huck, R.A. Alvarez-Puebla, L. the polymeric matrix of polysulfone microbeads. The synthesized M. Liz-Marzan, C. Abell, Microdroplet fabrication of silver-agarose composite material combines the high SERS activity resulting from nanocomposite beads for SERS optical accumulation, 7 (2011) 1321–1325. the plasmonic coupling of highly interacting nanoparticles and the [13] P. Aldeanueva-Potel, E. Faoucher, R.A. Alvarez-Puebla, L.M. Liz-Marzan, M. ability to accumulate analytes of the polysulfone porous support. Brust, Recyclable molecular trapping and SERS detection in silver-loaded This allows for the quantitative SERS detection down to the agarose gels with dynamic hot spots, Anal. Chem. 81 (2009) 9233–9238. nanomolar level, with a linear response that extends over an [14] S. Abalde-Cela, S. Ho, B. Rodríguez-González, M.A. Correa-Duarte, R.A. Álvarez- Puebla, L.M. Liz-Marzán, N.A. Kotov, Loading of exponentially grown LBL films impressive concentration range of five orders of magnitude. The with silver nanoparticles and their application to generalized SERS detection, novel synthetic strategy described herein overcomes the limita- Angew. Chem. Int. Edit. 48 (2009) 5326–5329. tions of the fabrication methods normally employed in the prepa- [15] M. Yang, R. Alvarez-Puebla, H.-S. Kim, P. Aldeanueva-Potel, L.M. Liz-Marzán, N. A. Kotov, SERS-active gold lace nanoshells with built-in hotspots, Nano Lett. 10 ration of composite plasmonic/polymeric materials, such as the (2010) 4013–4019. low nanoparticle loading capacity (around 1% as compared with [16] J. Zhang, S. Xu, E. Kumacheva, Polymer microgels: reactors for , the total weight of the composite) and the low porosity of the poly- metal, and magnetic nanoparticles, J. Am. Chem. Soc. 126 (2004) 7908–7914. [17] A.A. Farah, R.A. Alvarez-Puebla, H. Fenniri, Chemically stable silver meric matrix, which hampers the analyte diffusion inside the nanoparticle-crosslinked polymer microspheres, J. Coll. Interface Sci. 319 microbead. We can foresee that future work will be directed (2008) 572–576. 134 A. Trojanowska et al. / Journal of Colloid and Interface Science 460 (2015) 128–134

[18] T. Von Werne, T.E. Patten, Preparation of structurally well-defined polymer- [27] K.S.W. Sing, D.H. Everett, R.A.W. Haul, L. Moscou, R.A. Pierotti, J. Rouquerol, T. nanoparticle hybrids with controlled/living radical , J. Am. Siemieniewska, Reporting physisorption data for / systems with Chem. Soc. 121 (1999) 7409–7410. special reference to the determination of surface area and porosity [19] M. Mulder, Membrane preparation | phase inversion membranes, in: I.D. (Recommendations 1984), Pure Appl. Chem. 57 (1985) (1984) 603–619. Wilson (Ed.), Encyclopedia of Separation Science, Academic Press, Oxford, [28] R.C. Bansal, M. Goyal, Activated Adsorption, CRC Press, 2010. 2000, pp. 3331–3346. [29] B. Peña, L.C. De Menorval, R. Garcia-Valls, T. Gumí, Characterization of [20] C. Panisello, R. Garcia-Valls, Polysulfone/vanillin microcapsules production polysulfone and polysulfone/vanillin microcapsules by 1H NMR based on vapor-induced phase inversion precipitation, Ind. Eng. Chem. Res. 51 spectroscopy, solid-state 13C CP/MAS-NMR spectroscopy, and N2 (2012) 15509–15516. adsorption–desorption analyses, ACS Appl. Mater. Interfaces 3 (2011) 4420– [21] B. Peña, C. Panisello, G. Aresté, R. Garcia-Valls, T. Gumí, Preparation and 4430. characterization of polysulfone microcapsules for perfume release, Chem. Eng. [30] J. Landers, G.Y. Gor, A.V. Neimark, Density functional theory methods for Sci. 179 (2012) 394–403. characterization of porous materials, Colloid Surf. A – Physicochem. Eng. Asp. [22] C. Torras, L. Pitol-Filho, R. Garcia-Valls, Two methods for morphological 437 (2013) 3–32. characterization of internal microcapsule structures, J. Memb. Sci. 305 (2007) [31] B. Mir-Simon, I. Reche-Perez, L. Guerrini, N. Pazos-Perez, R.A. Alvarez-Puebla, 1–4. Universal one-pot and scalable synthesis of SERS encoded nanoparticles, [23] N. Pazos-Perez, F.J. Garcia de Abajo, A. Fery, R.A. Alvarez-Puebla, From nano to Chem. Mater. 27 (2015) 950–958. micro: synthesis and optical properties of homogeneous spheroidal gold [32] S.A. Gordeyev, G.Y. Nikolaeva, K.A. Prokhorov, R. Withnall, I.R. Dunkin, S.J. particles and their superlattices, Langmuir 28 (2012) 8909–8914. Shilton, P.P. Pashinin, Super-selective polysulfone hollow fibre membranes for [24] M. Grzelczak, J. Perez-Juste, P. Mulvaney, L.M. Liz-Marzan, Shape control in gas separation: assessment of molecular orientation by Raman spectroscopy, gold nanoparticle synthesis, Chem. Soc. Rev. 37 (2008) 1783–1791. Laser Phys. 11 (2001) 82–85. [25] M. Moskovits, Rev. Mod. Phys. 57 (1985) 783–826. [33] H.Y. Jung, Y.-K. Park, S. Park, S.K. Kim, Surface enhanced Raman scattering from [26] D.-Y. Wu, X.-M. Liu, S. Duan, X. Xu, B. Ren, S.-H. Lin, Z.-Q. Tian, Chemical layered assemblies of close-packed gold nanoparticles, Anal. Chim. Acta 602 enhancement effects in sers spectra: a quantum chemical study of pyridine (2007) 236–243. interacting with copper, silver, gold and platinum metals, J. Phys. Chem. C 112 (2008) 4195–4204.