Stability Of Self-assembled Monolayers Research Articles

Long‐term stability of self‐assembled monolayers on electropolished L605 cobalt chromium alloy for stent applications

Commercially available drug-eluting stents have the potential to induce inflammatory and hypersensitive adverse reactions due to their polymer coating. The use of self assembled monolayers (SAMs) as an alternate drug delivery platform for stents has recently been demonstrated. In this study, the formation and stability of phosphonic acid SAMs were investigated using the material and surface preparation commonly used to make ultra-thin stent struts-electropolished L605 Cobalt Chromium (CoCr) alloy. Methyl (⁻CH₃) and carboxylic acid (⁻OOH) terminated phosphonic acid SAMs were coated on electropolished CoCr alloy using a combination of solution immersion and dip-evaporation cycle deposition methods. SAMs-coated CoCr alloy specimens were thoroughly characterized using contact angle goniometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). These characterizations suggested that uniform and well-ordered monolayers were coated on the electropolished CoCr alloy. The long-term physiological stability of monolayers was investigated in tris-buffered saline (TBS) at 37°C for up to 28 days. Contact angles, FTIR, XPS, and AFM suggested that both ⁻CH₃ and ⁻COOH terminated phosphonic acid SAMs desorb from electropolished CoCr alloy surfaces in a biphasic manner. A significant desorption of ⁻CH₃ and ⁻COOH terminated SAMs occurs within 1-3 days followed by a slower desorption for up to 28 days. Thus, there is a need to develop techniques that can improve the long-term stability of SAMs on electropolished CoCr alloy for stent and other biomedical applications.

Corrosion Resistant Performances of Alkanoic and Phosphonic Acids Derived Self-Assembled Monolayers on Magnesium Alloy AZ31 by Vapor-Phase Method

Alkanoic and phosphonic acid derived self-assembled monolayers (SAMs) were formed on magnesium alloy by the vapor phase method. AFM and XPS studies showed that SAMs were formed on Mg alloy. The chemical and anticorrosive properties of the SAMs prepared on magnesium alloys were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. Water contact angle measurements revealed that, although SA and ISA have the same headgroup to anchor to the magnesium alloy surface, the packing density on the magnesium alloy surface could be considerably different. The contact angle hysteresis of SAMs with a carboxylate headgroup is much larger than that of SAMs with a phosphonic acid group. The XPS O 1s peaks indicated more likely a mix of mono-, bi-, or tridentate binding of phosphonic acid SAM to the oxide or hydroxide surface of the Mg alloy. The electrochemical measurements showed that the phosphonic acid derived SAM had better corrosion resistance compared to alkanoic acid derived SAM. The chemical stability of SAMs modified magnesium alloy was investigated using water contact angle and XPS measurements. The water contact angle and XPS measurements revealed that the molecular density of OP and PFEP on magnesium alloy would be higher than those of SA and ISA on magnesium alloy.

Control and stability of self-assembled monolayers under biosensing conditions

The ability to stabilize and control the attachment of cells on the surfaces of a variety of inorganic materials is important for the development of biomedical devices and sensors. An important intermediate step is the functionalization of semiconducting surfaces with a self-assembled monolayer (SAM) with an appropriate surface termination to interact with proteins. The stability of such SAMs is critical to withstanding subsequent processing and measurement conditions (e.g. long exposure to a buffer solution) to avoid artifacts resulting from such deterioration during electrical measurements. This work highlights the importance of surface cleaning and SAM chain length by comparing two commonly used short alkyl chains, aminopropyltriethoxysilane (APTES) or 3-(trimethoxysilyl)propyl aldehyde (C4-ald) molecules, with their long-chain counterparts, amino-undecilenyltriethoxysilane (AUTES) and 11-(triethoxysilyl)undecanal (C11-ald). Using IR spectroscopy, spectroscopic ellipsometry, and electrical measurements, a cleaning method is developed, based on a short room temperature (RT) SC-1 treatment, to remove photoresist without degrading device performance as is the case with currently used oxygen plasma methods. The spectroscopic and electrical measurements also show that short-chain SAMs, typically used for pH- or bio-sensing, do not have the stability suitable for biosensor environments. In contrast, long-chain SAMs display much higher stability and can be reproducibly grafted. These findings are the basis for a reliable preparation and robust operation of biosensors.

Theoretical study of the structure of self-assembled monolayers of short alkylthiolates on Au(111) and Ag(111): the role of induced substrate reconstruction and chain–chain interactions

We compare the stability of various structures of high coverage self-assembled monolayers (SAMs) of short alkylthiolates, S(CH(2))(n-1)CH(3) (= C(n)), on Ag(111) and Au(111). We employ: (i) the ab initio thermodynamics approach based on density functional theory (DFT) calculations, to compare the stability of SAMs of C(1) (with coverages Θ = 3/7 and 1/3) on both substrates, and (ii) a set of pairwise interatomic potentials derived from second-order Møller-Plesset (MP2) perturbation theory calculations, to estimate the role of chain-chain (Ch-Ch) interactions in the structure and stability of SAMs of longer chain alkylthiolates. For C(1)/Ag(111) (C(1)/Au(111)) the SAM with Θ = 3/7 is more (less) stable than for Θ = 1/3 in a wide range of temperatures and pressures in line with experiments. In addition, for the molecular densities of SAMs corresponding to Θ = 3/7 and 1/3, the MP2-based Ch-Ch interaction potential also predicts the different chain orientations observed experimentally in SAMs of alkylthiolates on Ag(111) and Au(111). Thus, for short length alkylthiolates, a simple model based on first principles calculations that separately accounts for molecule-surface (M-S) and Ch-Ch interactions succeeds in predicting the main structural differences between the full coverage SAMs usually observed experimentally on Ag(111) and Au(111).

Photocurrent generation through peptide‐based self‐assembled monolayers on a gold surface: antenna and junction effects

The photocurrent generation properties of mono- and bi-component peptide-based self-assembled monolayers (SAMs) immobilized on a gold surface were studied by electrochemical and spectroscopic techniques. The peptides investigated comprised almost exclusively C-tetrasubstituted -amino acids. These non-coded residues, because of their unique conformational properties, forced the peptide backbone to attain a helical conformation, as confirmed by X-ray crystal structure and CD determinations in solution. The peptide helical structure promoted the formation of a stable SAM on the gold surface, characterized by an electric macrodipole directed from the C(δ−) to the N(δ+) terminus, that remarkably affected the electron transfer (ET) process through the peptide chain. The peptides investigated were derivatized with chromophores strongly absorbing in the UV region to enhance the efficiency of the photocurrent generation (antenna effect). The influence of the nature of the peptide–gold interface on the ET process (junction effect) was analyzed by comparing the photocurrent generation process in peptide SAMs immobilized on a gold surface through AuS linkages with that in a bi-component SAM embedding a photoactive peptide into the linked palisade formed by disulfide-functionalized peptides.

The stability of self‐assembled monolayers with time and under biological conditions

The stability of self-assembled monolayers (SAMs) of different functionalities (CH(3)-, OH-, and EG4-) over time under appropriate storage conditions and when immersed in cell culture media was evaluated. X-ray photoelectron spectroscopy (XPS) was used to detect the oxidized sulfur species (S(2p) binding energy from 167 to 168 eV) resulting from oxidation of the surfaces. CH(3)-terminated SAMs stored for a period of 9 weeks in a nitrogen chamber were not altered. The same did not happen with OH- and EG4-SAMs, for which the XPS spectra evidenced oxidized peaks after 2 weeks. Regarding the stability of these surfaces under biological conditions, 30 min of immersion at 37 degrees C in serum-free or 10% fetal bovine serum (FBS) supplemented medium did not induce detectable oxidation. However, a small percentage of oxidized sulfur could have been washed out by the media, as confirmed in studies using SAMs immersed in water. Despite the possible rinsing out of oxidized thiols, high amounts of oxidation can still be detected by XPS. SAMs degradation during ethanol sterilization was not detectable by XPS, although a small increase on the wettability of OH-SAMs was observed. The data suggest that SAMs must be used freshly prepared, being recommended for short-term biological studies.

Potential control characteristics of short-chain thiols of thioctic acid and mercaptohexanol self-assembled on gold

In this article we systematically investigated self-assembly of short-chain thiols of thioctic acid (TA) and mercaptohexanol (MCH) on gold under potential control, E dc (−0.4, +0.4 and +0.7 V) and compared the results obtained with open circuit potential ( E OCP). Effect of E dc on thiol self-asembly was inspected based on the changes in electrochemical parameters including interfacial capacitance ( C), phase angle ( Φ 1 Hz), current density difference (Δ i), charge transfer resistance ( R ct) through cyclic voltammetry ( CV) and electrochemical impedance spectroscopy ( EIS). Experimental results showed that E dc could not obtain stable short-chain self-assembled monolayers (SAMs) (TA and MCH) in a short time. Both TA and MCH had slow self-assembly dynamics and needed a long time (> 24 h) to achieve adsorption equilibrium. Furthermore, the negative potential E dc (−0.4 V) did not facilitate the ordering of SAMs. The ordering of TA-SAMs was found to be the best when assembled under E dc (+0.4 V), whereas that of MCH-SAMs was almost the same when assembled under either E OCP or E dc (+0.4, +0.7 V). We considered that permeation of ions and water molecules perhaps dominated the slow self-assembly dynamics of short-chain thiols (TA and MCH) under E dc and mutual interaction between adjacent chains of thiols played an important role in the ordering of SAMs.

Modification of Electronic Properties of Graphene with Self-Assembled Monolayers

Integration of organic and inorganic electronic materials is one of the emerging approaches to achieve novel material functionalities. Here, we demonstrate a stable self-assembled monolayer of an alkylsilane grown at the surface of graphite and graphene. Detailed characterization of the system using scanning probe microscopy, X-ray photoelectron spectroscopy, and transport measurements reveals the monolayer structure and its effect on the electronic properties of graphene. The monolayer induces a strong surface doping with a high density of mobile holes (n > 10(13) cm(-2)). The ability to tune electronic properties of graphene via stable molecular self-assembly, including selective doping of steps, edges, and other defects, may have important implications in future graphene electronics.

Application of mass fabricated silicon-based gold transducers for amperometric biosensors

The backside contact, silicon-based transducers with vacuum-deposited gold layer (BSC) are evaluated as the base for electrochemical biosensors construction. Their comparison with commercially available transducers with screen printed gold and traditional gold disc electrode is reported. To determine the advantages and disadvantages of each of gold surfaces mentioned above, the 6-(ferrocenyl)-hexanethiol was used as the indicator. The results revealed the usefulness of BSC chips for the formation of stable self-assembled monolayers (SAMs). After the preliminary analysis, the SAM of thiol-ssDNA was formed on the BSC transducers as recognition layer. The electrochemical analysis in methylene blue solution was carried out after ssDNA immobilization and DNA–DNA hybridization. It is shown that prepared sensors are able to recognize complementary DNA sequence, based on the change in height and the potential shifts of reduction peaks of methylene blue. Obtained results are in full agreement with literature data. The compact size of silicone-based transducers allows to significantly reduce the required volume of tested solutions.

Long-term stability of self-assembled monolayers on 316L stainless steel

316L stainless steel (316L SS) has been extensively used for making orthopedic, dental and cardiovascular implants. The use of phosphonic acid self-assembled monolayers (SAMs) on 316L SS has been previously explored for potential biomedical applications. In this study, we have investigated the long-term stability of methyl (−CH3) and carboxylic acid (−COOH)-terminated phosphonic acid SAMs on 316L under physiological conditions. The stability of SAMs on mechanically polished and electropolished 316L SS was also investigated as a part of this study. Well-ordered and uniform −CH3- and −COOH-terminated SAMs were coated on mechanically polished and electropolished 316L SS surfaces. The long-term stability of SAMs on 316L SS was investigated for up to 28 days in Tris-buffered saline (TBS) at 37 °C using x-ray photoelectron spectroscopy, atomic force microscopy and contact angle goniometry. A significant amount of phosphonic acid molecules was desorbed from the 316L SS surfaces within 1 to 7 days of TBS immersion followed by a slow desorption of molecules over the remaining days. The −COOH-terminated SAM was found to be more stable than the −CH3-terminated SAM on both mechanically and electropolished surfaces. No significant differences in the desorption behavior of SAMs were observed between mechanically and electropolished 316L SS surfaces.

Influence of hydrogen bonds and double bonds on the alkane and alkene derivatives self-assembled monolayers on HOPG surface: STM observation and computer simulation

The adsorption structure and hydrogen-bonded complexes of alkane and alkene derivatives self-assembled on HOPG were studied by scanning tunneling microscopy (STM) and Molecular Mechanics (MM) simulations. The effect of different interior –CH CH– conformations and functional groups in molecules on the structure and stability of self-assembled monolayers was considered. It was found that octadecanol and trans-oleic acid could form stable structure on HOPG and their high-resolution images could be obtained by STM. Octadecanol exhibited two kinds of packing by alkyl–alkyl and adsorbate–substrate interactions. The interior trans–CH CH– group in trans-oleic acid had a slight influence on the self-assembly configuration. However, owing to the cis-double bond in the interior of cis-oleyamine molecule, the ordered monolayer could not be easily imaged by STM at ambient conditions. The adsorption conformations of three kinds of molecules on HOPG surface were optimized by MM simulation, respectively. The analysis of hydrogen-bond interactions by computation stimulation also revealed that the stability of cis-oleyamine on HOPG was the worst. These results demonstrated that molecular self-assembly and its stability could be significantly tailored by changing the molecular structure.

Stability of antibacterial self-assembled monolayers on hydroxyapatite

Open fractures are common in battlefields, motor vehicle accidents, gunshot wounds, sports injuries, and high-energy falls. Such fractures are treated using hydroxyapatite (HA)-based bone graft substitutes. However, open fracture wounds are highly susceptible to bacterial infections. Hence, this study was focused on incorporating antibacterial properties to HA using silver (Ag) carrying self-assembled monolayers (SAMs). Also, the stability of Ag carrying SAMs on HA was investigated under sterilization and physiological conditions. Initially, the -COOH terminated phosphonic acid SAMs of two different chain lengths (11 carbon atoms - shorter chain and 16 carbon atoms - longer chain) were deposited on HA. Antibacterial SAMs (ASAMs) were prepared by chemically attaching Ag to shorter and longer chain SAMs coated HA. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle goniometry collectively confirmed the attachment of Ag onto SAMs coated HA. The bacterial adhesion study showed that the adherence of Staphylococcus aureus was significantly reduced on ASAMs coated HA when compared to control-HA. The stability studies showed that gas plasma, dry heat and autoclave degraded most of the ASAMs on HA. UV irradiation did not damage the shorter chain ASAMs as vigorously as other treatments, while it degraded the longer chain ASAMs completely. Ethylene oxide treatment did not degrade the longer chain ASAMs unlike all other treatments but it severely damaged the shorter chain ASAMs. Both shorter and longer chain ASAMs significantly desorbed from the HA surfaces under physiological conditions although longer chain ASAMs exhibited better stability than shorter chain ASAMs. This study demonstrated the potential for using ASAMs to provide antibacterial properties to HA and the need for developing techniques to improve stability of SAMs under sterilization and physiological conditions.

Surface Functionalization of Zinc Oxide by Carboxyalkylphosphonic Acid Self-Assembled Monolayers

Two carboxyalkylphosphonic acids (HOOC(CH(2))(n)P(O)(OH)(2), n = 2 for 3-PPA and n = 9 for 10-PDA) have been deposited onto 1D zinc oxide (ZnO) nanowires and bare ZnO wafers to form stable self-assembled monolayers (SAMs). The samples were systematically characterized using wettability, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). 3-PPA was bound to the ZnO surfaces mainly through the CO(2)H headgroup, and 10-PDA formed self-assembled monolayers on the nanoscaled ZnO surface through the PO(3)H(2) headgroups. To verify the potential utilization of the functionalized surfaces in the construction of biosensors or bioelectronics, IgG (immunoglobulin G) protein immobilization through SAM bridging was demonstrated. This work expands the application of phosphonic acid-based surface functionalization on sensing and optoelectronic devices.

Thermal stability of thiol and silane monolayers: A comparative study

The stability of self-assembled monolayers (SAMs) at elevated temperatures is of considerable technological importance. The thermal stability of 1-octadecanethiol (ODT), 16-mercaptohexadecanoic acid (MHDA) and 1H,1H,2H,2H-perfluorodecanethiol (PFDT) SAMs on gold surfaces, and of 4-aminobutyltriethoxysilane (ABTES) and 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PFDS) assembled on hydroxylated silicon surfaces, was studied by X-ray photoelectron spectroscopy (XPS). The samples were heated in ultrahigh vacuum to temperatures in excess of that required for SAM degradation. ODT monolayers were stable to ca. 110 °C, while MHDA and PFDT SAMs were stable to ca. 145 °C. ABTES SAMs were found to be indefinitely stable to 250 °C, while PFDS SAMs were stable to 350 °C. These studies demonstrate the advantages of using silane monolayers for moderate to high temperature applications and illustrate differences that arise due to the nature of the tail group. To demonstrate the feasibility of silanes for template-directed patterning, a hydroxylated silicon oxide surface containing microcontact-printed PFDS patterns was spin-coated with a mainly hydrophilic block copolymer. Annealing the surface at 90 °C for 2 h caused the block copolymer to dewet the hydrophobic PFDS-patterned regions and adsorb exclusively on the unpatterned regions of the surface.

Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

Spontaneous adsorption of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4α-Co IITAPc) on glassy carbon (GC) electrode leads to the formation of a stable self-assembled monolayer (SAM). Since the SAM of 4α-Co IITAPc is redox active, its adsorption on GC electrode was followed by cyclic voltammetry. SAM of 4α-Co IITAPc on GC electrode shows two pairs of well-defined redox peaks corresponding to Co III/Co II and Co IIIPc −1/Co IIIPc −2. The surface coverage ( Γ) value, calculated by integrating the charge under Co II oxidation, was used to study the adsorption thermodynamics and kinetics of 4α-Co IITAPc on GC surface. Cyclic voltammetric studies show that the adsorption of 4α-Co IITAPc on GC electrode has reached the saturation coverage ( Γ s) within 3 h. The Γ s value for the SAM of 4α-Co IITAPc on GC electrode was found to be 2.37 × 10 −10 mol cm −2. Gibbs free energy (Δ G ads) and adsorption rate constant ( k ad) for the adsorption of 4α-Co IITAPc on GC surface were found to be −16.76 kJ mol −1 and 7.1 M −1 s −1, respectively. The possible mechanism for the self-assembly of 4α-Co IITAPc on GC surface is through the addition of nucleophilic amines to the olefinic bond on the GC surface in addition to a meager contribution from π stacking. The contribution of π stacking was confirmed from the adsorption of unsubstituted phthalocyanatocobalt(II) (CoPc) on GC electrode. Raman spectra for the SAM of 4α-Co IITAPc on carbon surface shows strong stretching and breathing bands of Pc macrocycle, pyrrole ring and isoindole ring. Raman and CV studies suggest that 4α-Co IITAPc is adopting nearly a flat orientation or little bit tilted orientation.

Self-assembly of methanethiol on the reconstructed Au(111) surface

We present a combined experimental and theoretical study of molecular methanethiol $({\text{CH}}_{3}\text{SH})$ adsorption on the reconstructed Au(111) surface in the temperature range between 90 and 300 K in UHV. We find that the simplest thiol molecules form two stable self-assembled monolayer (SAM) structures that are created by distinct processes. Below 120 K, a solid rectangular phase, preserving the herringbone reconstruction, emerges from individual chains of spontaneously formed dimers. At higher adsorption temperatures below 170 K, a close-packed phase forms via dissociative ${\text{CH}}_{3}\text{SH}$ adsorption and the formation of Au adatoms that are not incorporated into the SAM. We show that the combination of a strong substrate-mediated interaction with nondissociative dimerization and temperature activated removal of the Au(111) reconstruction drives the large-scale assembly of molecular ${\text{CH}}_{3}\text{SH}$ into two distinct phases.

Electrochemical Detection of Self-Assembled Viologen Modified Electrode as Mediator of Glucose Sensor

An amperometric glucose biosensor has been developed using viologen derivatives as a charge transfer mediator between a glucose oxidase (GOD) and a gold electrode. A highly stable self-assembled monolayer (SAM) of thiol-based viologen was immobilized onto the gold electrode of a quartz crystal microbalance (QCM) and GOD was immobilized onto the viologen modified electrode. This biosensor response to glucose was evaluated amperometrically in the potential of -300mV. Upon immobilization of the glucose oxidase onto the viologen modified electrode, the biosensor showed rapid response towards glucose. Experimental conditions influencing the biosensor performance, such as pH potential, were optimized and assessed. This biosensor offered excellent electrochemical responses for glucose concentration below <TEX>${\mu}$</TEX> mol level with high sensitivity and selectivity and short response time. The levels of the RSDs (<5%) for the entire analyses reflected the highly reproducible sensor performance. A linear calibration range between the current and the glucose concentration was obtained up to <TEX>$4.5{\times}10^{-4}M$</TEX>. The detection limit was determined to be <TEX>$3.0{\times}10^{-6}M$</TEX>.

Self-assembly of silanated poly(ethylene glycol) on silicon and glass surfaces for improved haemocompatibility

Surface immobilization of poly(ethylene glycol) (PEG) is an effective method to produce a material surface with protein repulsive property. This property could be made permanent by using covalent grafting of the PEG molecules onto material surfaces. In this study, self-assembled monolayers (SAMs) of PEG on silicon-containing materials (silicon chip and glassplate) were obtained through a one-step coating procedure of one kind of silanated PEG molecules made through the reaction between monomethoxy PEG and 3-isocyanatopropyltriethoxysilane. Atomic force microscopy (AFM) and water static contact angle measurement were employed to investigate the surface topography and wettability of the PEGylated material surfaces. The changes in the topography and the water contact angle of the surfaces with time of incubation in PBS solution were also measured. The results revealed that stable and uniform self-assembled monolayers of PEG could be formed on silicon or glass surfaces by simply soaking the substrates in the solution of silanated PEGs. The covalent coupling of PEGs to the substrates was also confirmed. In order to evaluate the stability of the SAMs, blood compatibility of the modified glassplate surface was evaluated by measuring full blood activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT), as well as by scanning electron microscopy (SEM) analysis of the appearance of adherence and denaturation of blood platelets onto the glassplate. The silanated PEGs were shown to have good effect on the protein-repulsion as well as haemocompatibility of the substrates.

Electric Potential Stability and Ionic Permeability of SAMs on Gold Derived from Bidentate and Tridentate Chelating Alkanethiols

The interfacial electrochemical properties of self-assembled monolayers (SAMs) on gold derived from a structurally tailored series of monodentate, bidentate, and tridentate chelating alkanethiols were investigated. Specific adsorbates included 1-hexadecanethiol (C16), 2-tetradecylpropane-1,3-dithiol (C16C2), 2-tetradecyl-2-methylpropane-1,3-dithiol (C16C3), 2,2-ditetradecylpropane-1,3-dithiol (C16C16), and 1,1,1-tris(mercaptomethyl)pentadecane (t-C16). Reductive desorption of the SAMs as a function of potential was probed by voltammetric measurements, which indicated the following relative order of electric potential stability: t-C16 > C16C2 ≈ C16C3 ≈ C16C16 > C16. The ionic permeability was investigated under various applied cathodic potentials by electrochemical impedance spectroscopy (EIS). An examination of SAMs prepared at room temperature and accessed by EIS at open-circuit potential showed that the ionic permeability increased in the order C16C2 < C16 < C16C3 < C16C16 < t-C16. The ionic permeability of films was further influenced by the electric potential of the metal substrate and the temperature at which the monolayers were assembled. The potential dependence of the ionic permeability was qualitatively rationalized by considering both the initial ionic permeability and the electric potential stability of the SAMs. Similarly, the ionic permeability of the SAMs prepared at elevated temperature showed contributions from both their thermal stability and their insulating properties at room temperature.

Surface modification of cobalt–chromium–tungsten–nickel alloy using octadecyltrichlorosilanes

Cobalt–chromium (Co–Cr) alloys have been extensively used for medical implants because of their excellent mechanical properties, corrosion resistance, and biocompatibility. This first time study reports the formation and stability of self-assembled monolayers (SAMs) on a Co–Cr–W–Ni alloy. SAMs of octadecyltrichlorosilanes (OTS) were coated on sputtered Co–Cr–W–Ni alloy thin film and bulk Co–Cr–W–Ni alloy. OTS SAM coated alloy specimens were characterized using contact angle goniometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Contact angle analysis and FTIR suggested that ordered monolayers were coated on both sputtered and bulk alloy. XPS suggested the selective dissolution of cobalt from the alloy during the formation of OTS SAM. The bonding between the alloy and the OTS SAM was mainly attributed to Si–O–Cr and Si–O–W covalent bonds and a smaller contribution from Si–O–Co bonds. AFM images showed the distribution of islands of monolayers coated on the alloy. The height of monolayers in majority of the islands was closer to the theoretical length of fully extended OTS molecules oriented perpendicular to the surface. The stability of OTS SAM was investigated in tris-buffered saline at 37 °C for up to 7 days. Contact angle, FTIR, and XPS collectively confirmed that the monolayers remain ordered and bound to the alloy surface under this condition. This study shows that Co–Cr alloys can be surface modified using SAMs for potential biomedical applications.