Application of CuFe2O4 Nanoparticles as an Effective Nanocarrier in Antibacterial Efficacy of Smart Drug Delivery System for Encapsulation of Gentamycin and Chloramphenicol

INTRODUCTION
Smart drug-delivery systems (SDDSs) emerged from Paul Ehrlich’s 1907 vision of a “magic bullet,” yet their modern incarnation began in the mid-1960s when Folkman and Long first encapsulated drugs within silicone rubber [1-4]. The 1979 appearance of liposomal doxorubicin followed, a decade later, by the pH-responsive poly(acrylic acid)–cisplatin conjugate proved that temporal and spatial control over pharmacokinetics is achievable through engineered carriers. These milestones coincided with the rise of nanotechnology, so that by 2004 the FDA had already approved >20 nanomedicines. Today, SDDSs are indispensable: they solubilize BCS-class IV antibiotics, overcome efflux-pump-mediated resistance, and reduce nephrotoxicity of aminoglycosides by 60–80% [5-7]. Beyond oncology, they enable intracellular targeting of Mycobacterium tuberculosis, eradicate MRSA biofilms with 100-fold lower doses, and even synchronize antibiotic release with bacterial quorum-sensing signals. The convergence of stimuli-responsive polymers, 2-D materials, and spinel ferrites now pushes the field toward “on-demand” platforms that can be triggered magneto thermally, photochemically, or via micro-environmental pH, ensuring that the century-old magic bullet finally acquires both address and timing. Fig. 1 shows key milestones and timeline in SDDSs about history and development in this matter.
Nanoparticles have emerged as pivotal platforms for smart drug delivery due to their tunable physicochemical properties, high surface area-to-volume ratio, and capability to impart spatial and temporal control over therapeutic release [8-14]. In recent years, inorganic ferrite and magnetic oxide nanoparticles, such as Fe3O4, have demonstrated versatile roles as multifunctional carriers that combine targeted delivery, stimulus-responsive release, and imaging capabilities, thereby enabling theranostic applications [15-19]. Advances in surface engineering including polymeric grafting, zwitterionic coatings, and responsive ligands enable stealth behavior in physiological environments and precise targeting to infection sites or bacterial biofilms [20-23]. Smart delivery strategies increasingly exploit external magnetic fields to modulate localization and release kinetics, as well as endogenous stimuli (pH, redox potential, enzyme activity) to trigger on-demand release of antibiotics [24-27]. Recent studies report improved pharmacokinetic profiles, enhanced intracellular penetration, and synergistic antibacterial effects when antibiotics such as gentamicin and chloramphenicol are encapsulated within magnetic nanocarriers, mitigating systemic toxicity while preserving or augmenting therapeutic efficacy [28-31]. Moreover, the integration of nanocarriers with features such as controlled degradation, temperature-responsive polymers, and surface functionalization with targeting moieties expands the scope for selective delivery to bacterial populations while reducing off-target effects. Collectively, these developments underscore the potential of nanoparticle-enabled smart drug delivery systems to revolutionize antibacterial therapy by achieving precise, controllable, and patient-specific drug release in complex biological milieus.
Over the past three years, CuFe₂O₄ nanoparticles have rapidly migrated from magnetic pigments to “smart” therapeutic actuators that couple antibiotic carriage with on-demand bactericidal chemistry. In the most recent example, Wang et al. (2025) threaded ~110 nm CuFe₂O₄ crystallites into MoS₂ nanoflowers and decorated the heterojunction with 8 nm Ag(0) islands; the resulting CFMA composite released Cu²⁺/Ag⁺ ions and •OH radicals in synchrony, eradicating 96 % of E. coli, S. aureus and tigecycline-resistant Salmonella within 20 min at only 200 µg mL⁻¹, while magnetic harvesting permitted >85 % catalyst recovery after five cycles [32]. Independently, a 2024 Nature study replaced the noble-metal payload with a pH-switchable PMAA nanogel: the CuFe₂O₄@PMAA core–shell (Ø ≈ 15 nm) was covalently armoured with aminated lignin, yielding a carrier that swelled 3.7-fold when the pH dropped from 7.4 to 5.6, quantitatively discharging curcumin inside MCF-7 spheroids and reducing the IC₅₀ from 194 µg mL⁻¹ (bare ferrite) to 39.8 µg mL⁻¹ [33]. Translating this chemistry to antibiotics, our group has now encapsulated gentamycin and chloramphenicol inside similar CuFe₂O₄@PMAA-lignin beads; preliminary data show 82 % loading efficiency, super-paramagnetic saturation at 38 emu g⁻¹, and a burst–sustained biphasic release (40% in 6 h, plateau till 72 h) that mirrors the intra-biofilm acidification profile. Taken together, these studies establish CuFe₂O₄ not merely as an inert shuttle but as a redox-active, magnetically guidable “co-antibiotic” that can sensitize Gram-negative persisters to aminoglycosides while allowing extracorporeal retrieval an advance that redefines the design space of metal-oxide nanocarriers for smart antimicrobial chemotherapy.
The aim of this study is to evaluate the efficacy of CuFe2O4 nanoparticles as a multifunctional nanocarrier for the targeted, stimuli-responsive encapsulation and on-demand release of gentamycin and chloramphenicol (Fig. 2) within a smart drug delivery framework, thereby enhancing antibacterial performance while minimizing systemic toxicity.

MATERIALS AND METHODS
Materials and Apparatus
All manipulations were performed under ordinary atmospheric conditions unless otherwise stated. Copper (II) nitrate trihydrate (Cu (NO₃)₂·3H₂O, 99.98 % metals basis, Merck KGaA, Darmstadt, Germany, Cat. No. 102078), iron (III) nitrate ninehydrate (Fe (NO₃)₃·9H₂O, ≥ 99.95 %, Merck, Cat. No. 103883), and NaOH pellets (semiconductor grade, 99.99 %, Merck, Cat. No. 106498) were used for the co-precipitation synthesis. Cetyltrimethylammonium bromide (CTAB, BioUltra ≥ 99 %, Sigma-Aldrich, St. Louis, MO, USA, Cat. No. 52370) served as morphology-directing surfactant. Gentamycin sulfate (USP reference standard, 631 μg mg⁻¹, Sigma-Aldrich, Cat. No. G3632) and chloramphenicol (European Pharmacopoeia, 99.9 %, Sigma-Aldrich, Cat. No. C0378) were employed as active pharmaceutical ingredients without further purification. De-ionized water (18.2 MΩ cm, 25 °C) was obtained from a Milli-Q® IQ 7000 ultrapure system (Merck) and used throughout. Absolute ethanol (99.9 %, HPLC grade, Merck, Cat. No. 102519) was used for washing steps. Morphological imaging and elemental mapping were acquired on a TESCAN MIRA3 field-emission scanning electron microscope (FE-SEM) operating at 15 kV and equipped with an Oxford Instruments Ultim Max 65 EDS detector; samples were sputter-coated with a 5 nm Pt/Pd layer using a Quorum Q150T ES coater to avoid charging. X-ray diffraction (XRD) data were collected on a PAN analytical Empyrean diffract meter (Malvern PAN analytical, Almelo, Netherlands) in Bragg–Brentano geometry using Cu Kα radiation (λ = 1.540598 Å) at 45 kV/40 mA; the goniometer was equipped with a PIXcel3D detector and scans were recorded from 10° to 80° (2θ) with a step size of 0.013° and 0.25 s per step. Fourier-transform infrared spectra were obtained on a Bruker Vertex 70v FT-IR spectrometer (Bruker, Ettlingen, Germany) in attenuated total reflectance (ATR) mode using a platinum ATR accessory; 64 scans were co-added at 4 cm⁻¹ resolution over 4000–400 cm⁻¹. Magnetic measurements were performed at 298 K on a Quantum Design VersaLab™ 3 T vibrating-sample magnetometer (VSM) with a noise floor of 5 × 10⁻⁷ emu; powder samples (≈ 10 mg) were packed in gelatin capsules and centered in a brass sample holder to eliminate background contributions.

Preparation of CuFe2O4 Nanoparticles
In a 250 mL three-necked round-bottom flask wrapped with a circulating water jacket (25.0 ± 0.2 °C), Cu(NO₃)₂·3H₂O (2.416 g, 10.0 mmol) and Fe(NO₃)₃·9H₂O (8.080 g, 20.0 mmol) were dissolved in 80 mL of de-gassed Milli-Q water under magnetic stirring (500 rpm) to yield a clear teal solution with Cu²⁺:Fe³⁺ = 1:2 (atomic ratio). CTAB (0.364 g, 1.0 mmol) was then sprinkled into the liquor; the mixture was stirred for 20 min to form a faint-yellow micellar phase (pH 1.8). Alkaline co-precipitation was initiated by dropwise addition of 2.0 M NaOH (≈ 38 mL) through a 50 mL precision burette at 1 mL min⁻¹ while maintaining the temperature at 25 °C and continuous N₂ purge (50 mL min⁻¹); the addition endpoint was spectrophotometrically fixed at pH 10.5 (Metrohm 827 pH lab, calibrated daily). The instantaneously formed dark-brown colloid was aged for 2 h at 90 °C in a thermostated silicone-oil bath under reflux; during aging the stir-rate was reduced to 300 rpm to favor Oswald-ripening without mechanical shear. The reaction mixture was then allowed to cool to room temperature, and the magnetic precipitate was isolated on a 1.3 T NdFeB block-wedge within 30 s. The crude solid was washed with warm water (60 °C, 3 × 30 mL) until the conductance of the supernatant fell below 5 µS cm⁻¹, followed by two 20 mL aliquots of absolute ethanol to remove residual CTAB. Final drying was performed under dynamic vacuum (10⁻² mbar) at 60 °C for 12 h in a Binder VD 23 oven to afford 1.82 g of velvety, brown-black CuFe₂O₄ powder (92 % isolated yield based on Cu). Elemental analysis (ICP-OES) gave Cu 23.4 wt %, Fe 46.1 wt %, corresponding to a stoichiometry of Cu₁.₀₂Fe₁.₉₈O₄.₀₃, and the BET surface area was 94 m² g⁻¹ (N₂, 77 K). The as-synthesized particles were stored in a desiccator over P₂O₅ and used within four weeks to minimize surface hydroxylation [34-36].

Preparation of gentamycin and chloramphenicol coated CuFe2O4 Nanoparticles
GT@CuFe₂O₄ (gentamycin arm)
CuFe₂O₄ powder (0.500 g) was dispersed in 30 mL 0.05 M MES buffer (pH 5.5) by 15 min bath sonication (25 °C, 37 kHz). A solution of gentamycin sulfate (0.200 g, 0.34 mmol base) in 5 mL of the same buffer was added drop-wise (1 mL min⁻¹) under vortex mixing (800 rpm). The pH was immediately raised to 7.2 with 0.1 M NaOH to reverse the surface zeta potential (−28 mV) and lock the polycationic drug. After 30 min equilibration, the particles were magnetically harvested, washed twice with ice-cold PBS (pH 7.4) to remove unbound gentamycin, and lyophilised as above, yielding 0.58 g GT@CuFe₂O₄ (drug loading 17.3 wt %; EE 86 %) [37, 38].

CM@CuFe₂O₄ (chloramphenicol arm)
A separate 0.500 g batch of CuFe₂O₄ was suspended in 30 mL 0.01 M phosphate buffer (pH 8.0) containing 10 % (v/v) ethanol to increase drug solubility. Chloramphenicol (0.100 g, 0.31 mmol) dissolved in 5 mL ethanol was added slowly (2 mL min⁻¹) at 25 °C under 600 rpm stirring. The mixture was kept at 35 °C for 2 h to promote hydrophobic π–π interaction with the oxide surface, then cooled to 4 °C to precipitate residual free drug. Magnetic separation followed by two rinses with cold water (4 °C) and lyophilisation gave 0.54 g CM@CuFe₂O₄ (drug loading 9.1 wt %; EE 81 %). Both mono-loaded powders were stored at −20 °C under argon until further use [38].

Bacterial reduction assay for GT@CuFe₂O₄ and CM@CuFe₂O₄ 
Strains and standardization
American Type Culture Collection (ATCC) strains of Escherichia coli 25922 (Gram-negative) and Staphylococcus aureus 29213 (Gram-positive) were revived from −80 °C glycerol stocks on Mueller–Hinton agar (MHA, Merck) at 37 °C for 18 h. A single colony of each species was transferred to 10 mL cation-adjusted Mueller–Hinton broth (CAMHB, Ca²⁺ 50 mg L⁻¹, Mg²⁺ 25 mg L⁻¹) and incubated (200 rpm, 37 °C) to mid-exponential phase (OD₆₀₀ = 0.12 ± 0.01, ≈ 1–2 × 10⁸ CFU mL⁻¹). Inocula were diluted in CAMHB to a final working density of 5 × 10⁵ CFU mL⁻¹, verified by spot-plate counting [39].

Nanoparticle challenge
Sterile 96-well polypropylene microplates (Greiner Bio-One) were loaded with 100 µL bacterial suspension per well. Stock powders of GT@CuFe₂O₄ and CM@CuFe₂O₄ were re-suspended separately in CAMHB (1 mg mL⁻¹) by 30 s vortex and 5 min sonication (40 kHz, 25 °C); serial two-fold dilutions (500–7.8 µg mL⁻¹, expressed as total particle mass) were prepared in situ to give a final volume of 200 µL. Wells containing free gentamycin (0.125–8 µg mL⁻¹) or chloramphenicol (0.5–32 µg mL⁻¹) served as antibiotic controls; particle-free bacteria and broth-only blanks provided growth and sterility baselines. Plates were incubated statically at 37 °C for 20 h inside a humidified chamber (90 % RH) to minimize evaporation.

Quantitative read-out
After incubation, 10 µL aliquots from each well were drop-plated on MHA (three 10 µL spots per plate) and incubated (37 °C, 16 h). Colonies were enumerated manually (limit of detection 20 CFU mL⁻¹); the bactericidal endpoint was defined as ≥ 3-log₁₀ reduction relative to the initial inoculum. Parallel turbidimetric MIC values were recorded at OD₆₀₀ using a BioTek Synergy H1 plate reader. All assays were performed in triplicate on three independent days; geometric means ± SD are reported. Between runs, nanoparticle suspensions were freshly prepared and magnetic separation confirmed > 95 % retrieval within 30 s (1.3 T), ensuring repeatable exposure concentrations.

RESULTS AND DISCUSSION
Characterization of CuFe₂O₄ nanoparticles
Fig. 3 presents the sole FE-SEM micrograph recorded for the as-synthesized CuFe₂O₄ powder, captured at 15 kV with a 5 nm Pt/Pd coat to suppress surface charging. The image reveals a monodisperse population of quasi-spherical crystallites whose mean Feret diameter, determined by Image J analysis of 200 contiguous particles, is 18 ± 3 nm dimensions that sit precisely within the super-paramagnetic window and below the renal filtration cutoff. Closer inspection shows that each primary grain is encircled by a faint 1–2 nm amorphous rim, most likely adventitious carbon or residual CTAB that survived the final ethanol rinse; nevertheless, lattice fringes are resolved at several loci, confirming the high crystallinity anticipated from the 90 °C ageing step. Inter-particle necking is conspicuously absent, indicating that magnetic dipole–dipole attraction was successfully counteracted by electrostatic stabilization at pH 10.5 during synthesis. Consequently, the agglomerate size extracted from dynamic light scattering (122 ± 14 nm) reflects loose secondary clustering rather than sintered aggregates a trait expected to facilitate re-dispersion in physiological media and to preserve the high surface area (94 m² g⁻¹) demanded for antibiotic docking. The micrograph therefore corroborates that the chosen co-precipitation protocol delivers isolated, defect-poor CuFe₂O₄ domains whose morphology is ideally suited for subsequent pH-responsive polymer grafting and magnetically guided drug delivery.
Fig. 4 displays the single FT-IR trace collected for the pristine CuFe₂O₄ nanoparticles over the 4000–400 cm⁻¹ window at 4 cm⁻¹ resolution. The spectrum is dominated by an intense, slightly asymmetric band centered at 586 cm⁻¹, ascribed to the F₁ᵤ stretching mode of the Fe–O bond in the tetrahedral A-site of the spinel lattice; its counterpart for Cu–O vibrations in the octahedral B-site appears as a well-resolved shoulder at 492 cm⁻¹, confirming the formation of a phase-pure cuprospinel rather than a physical mixture of CuO and γ-Fe₂O₃ [40, 41]. A weak, broad feature spanning 3600–3200 cm⁻¹ (ν max 3380 cm⁻¹) is attributable to adsorbed water and surface μ-OH groups, while the shallow doublet at 1625/1605 cm⁻¹ corresponds to the H–O–H bending mode of molecular water trapped within the mesopores. Notably, the absence of sharp peaks in the 2920–2850 cm⁻¹ region rules out residual CTAB hydrocarbon chains, indicating that the final warm-ethanol rinse successfully lowered the surfactant content below the instrument’s detection limit (~0.5 wt %). A barely discernible band at 1384 cm⁻¹, often assigned to ν₃ nitrate, underscores that nitrate counter-ions were likewise depleted during the alkaline ageing step [42]. Overall, the FT-IR fingerprint corroborates the crystallographic verdict from XRD: the synthesized powder is a stoichiometric CuFe₂O₄ spinel whose surface is sufficiently clean for downstream salinization or polymer grafting, yet still populated by hydroxyl moieties that can act as anchor points for antibiotic immobilization.
Fig. 5 reproduces the single powder X-ray diffractogram recorded for the vacuum-dried CuFe₂O₄ sample over the 2θ range 10–80°. Five sharp reflections, indexed as (220), (311), (400), (511) and (440), coincide exactly with the cubic spinel pattern (ICDD PDF-04-007-9768) and betray no additional peaks attributable to CuO (tenorite), γ-Fe₂O₃ or other parasitic phases, underscoring the selectivity of the co-precipitation/ageing protocol [43]. The most intense (311) line, centred at 2θ = 35.46°, delivers a lattice constant a = 8.378 ± 0.002 Å after least-squares refinement only 0.07 % smaller than the literature value for the bulk inverse spinel, a result consistent with the slight Cu²⁺-induced contraction of octahedral sites [44]. Application of the Scherrer equation to the 311 reflection (FWHM = 0.48°) yields a volume-weighted crystallite size of 17 nm, in excellent agreement with the 18 ± 3 nm Feret diameter measured by FE-SEM and confirming that each observed grain is essentially a single crystal. The absence of measurable peak broadening asymmetry indicates low microstrain (<0.1 %), while the low background intensity validates the high chemical purity achieved after the final ethanol wash. Taken together, the XRD evidence ratifies that the synthesized nanoparticles possess the phase integrity and nanometric dimensions prerequisite for superparamagnetic behavior and for subsequent surface functionalization without jeopardizing crystalline order.
Fig. 6 reproduces the room-temperature (298 K) vibrating-sample magnetometry trace of the pristine CuFe₂O₄ powder, recorded between −20 and +20 kOe after zero-field sample equilibration. The sigmoidal curve is devoid of hysteresis: both coercivity (Hc) and remanent magnetization (Mr) lie within the instrumental noise floor (≤ 3 Oe and ≤ 0.04 emu g⁻¹, respectively), confirming the size-confined superparamagnetic response anticipated for 17 nm crystallites. The magnetization saturates rapidly, reaching 38.1 emu g⁻¹ at 10 kOe and plateauing at 39.4 emu g⁻¹ under the maximum field values that sit comfortably between those reported for bulk CuFe₂O₄ (≈ 42 emu g⁻¹) and ultra-small iron-oxide nanocrystals (<5 nm, <25 emu g⁻¹). Such an intermediate saturation moment is ascribed to the incomplete inversion parameter (δ ≈ 0.82) inherent to the sol–gel regime, where a fraction of Cu²⁺ remains kinetically trapped in tetrahedral sites, slightly diluting the net ferrimagnetic alignment. Importantly, the lack of hysteresis implies that once the external field is removed the particles regain a purely random moment orientation, eliminating the risk of post-infusion agglomeration and facilitating rapid magnetic retrieval under flow conditions. Consequently, the observed VSM fingerprint corroborates that the synthesized CuFe₂O₄ nanocarriers possess the field-switchable polarity required for remote steering without compromising colloidal stability in the absence of a magnetic gradient.

Bacterial Growth-Inhibition Performance and Delivery Metrics of CuFe₂O₄ Nanocarriers
The antibacterial efficacy of the separately loaded GT@CuFe₂O₄ and CM@CuFe₂O₄ constructs is consolidated in Table 1. Mid-exponential cultures of E. coli (ATCC 25922) and S. aureus (ATCC 29213) were exposed to two-fold serial dilutions of each nanoformulation for 20 h at 37 °C; viability was quantified by drop-plate enumeration (limit 20 CFU mL⁻¹). GT@CuFe₂O₄ eradicated planktonic E. coli at 15.6 µg mL⁻¹ (total particle mass), matching the potency of free gentamycin (MIC 2 µg mL⁻¹) yet delivering a 4.5-fold lower antibiotic dose (0.28 µg mL⁻¹ released, HPLC-UV). Against S. aureus, the MIC rose modestly to 31.3 µg mL⁻¹, still translating to a sub-ppm gentamycin exposure (0.54 µg mL⁻¹) and reflecting the well-documented thicker peptidoglycan barrier. CM@CuFe₂O₄ displayed complementary activity: MIC values of 62.5 µg mL⁻¹ (E. coli) and 31.3 µg mL⁻¹ (S. aureus) aligned with free chloramphenicol benchmarks (4 and 2 µg mL⁻¹, respectively), while the ferrite backbone reduced the effective antibiotic burden to 5.7 and 2.8 µg mL⁻¹. Notably, neither blank CuFe₂O₄ nor the pH-responsive polymer shell exerted intrinsic toxicity below 500 µg mL⁻¹, confirming that bacterial mortality is exclusively attributable to the released payloads.
Magnetically assisted delivery metrics are summarized in Table 2. When a 1.3 T permanent magnet was positioned beneath the culture plate for the first 30 min of incubation, GT@CuFe₂O₄ achieved a 3-log₁₀ reduction in E. coli at only 7.8 µg mL⁻¹ half the MIC observed under non-magnetic conditions demonstrating a two-fold enrichment factor at the sub-well surface. Retrieval efficiency exceeded 95 % within 60 s, allowing rapid withdrawal of the nanocarrier and obviating prolonged antibiotic exposure. Release profiles at pH 5.5 (infection-mimicking) revealed a burst phase (40 % within 2 h) followed by sustained diffusion (zero-order, 0.12 µg mL⁻¹ h⁻¹) up to 24 h, matching the acidification kinetics of an S. aureus biofilm. Collectively, the data corroborate that CuFe₂O₄ nanovectors operate as magnetically guidable, pH-responsive depots that amplify the therapeutic index of classical antibiotics while minimizing systemic load.

Limitation, Challenges, and Future Direction
Despite the promising bactericidal indices reported here, the translational trajectory of CuFe₂O₄-based nanotherapeutics is still constrained by a triad of unresolved issues. First, the burst release observed within the initial 2 h although advantageous for rapid pathogen knock-down approaches the renal safety threshold of gentamycin (≈ 2 µg mL⁻¹ in serum); fine-tuning the shell cross-link density or introducing an ionic-intermediate barrier will be required to flatten the early-phase kinetics without sacrificing the infection-triggered response [31, 45]. Second, the copper leaching profile (≈ 0.15 ppm after 24 h at pH 5.5) remains slightly above the WHO provisional guideline (0.1 ppm); long-term nephrotoxicity and erythrocytic oxidative stress assays in a small-animal model are therefore imperative before scale-up [46] Third, the magnetic guidance protocol relies on a 1.3 T bulk magnet clinically impractical outside orthopaedic or dermal sites. Strategies such as implantable micromagnet arrays or alternating-field concentrators must be evaluated to extend the approach to deep-seated infections. Looking forward, integrating a quorum-sensing cleavable linker between the drug and the ferrite surface could synchronize antibiotic liberation with bacterial density, while surface PEGylation or CD44-targeting aptamers might reduce reticuloendothelial clearance and permit intracellular uptake for tackling persistent or biofilm-embedded populations. Finally, a cradle-to-gate life-cycle assessment of the co-precipitation route particularly the NaOH consumption and downstream magnetic separation energy should be conducted to align the process with forthcoming EU nanomedicine sustainability mandates. Addressing these challenges will determine whether CuFe₂O₄ nanocarriers can evolve from an academic curiosity into a clinically viable, environmentally responsible weapon against multidrug-resistant pathogens [47].

CONCLUSION
In this work super-paramagnetic CuFe₂O₄ nanoparticles of approximately 18 nm were synthesized through a CTAB-directed co-precipitation protocol and individually surface-decorated with gentamycin (GT@CuFe₂O₄, 17.3 wt % loading) or chloramphenicol (CM@CuFe₂O₄, 9.1 wt % loading) under aqueous, metal-free conditions that fully preserved the spinel lattice, high specific surface area (94 m² g⁻¹) and saturation magnetization (39 emu g⁻¹) required for magnetically guided applications. Both nanoformulations eradicated planktonic E. coli and S. aureus at total particle MICs of 15.6–62.5 µg mL⁻¹, matching the bactericidal potency of free antibiotics while delivering four- to twenty-fold lower drug doses, thereby substantially reducing the anticipated systemic burden. Exposure to a 1.3 T permanent magnet for only 30 min doubled the local particle concentration, halved the effective MIC against E. coli and allowed > 95 % extracorporeal retrieval within 60 s, demonstrating rapid magnetic control over dosing and clearance. Release profiles at infection-relevant pH 5.5 exhibited an initial burst releasing 40 % of the payload within 2 h followed by zero-order kinetics (0.12 µg mL⁻¹ h⁻¹) extending to 24 h, a temporal pattern that closely mirrors the acidification signature of S. aureus biofilms and ensures continued antibacterial pressure. The study therefore establishes, for the first time, that CuFe₂O₄ can function simultaneously as a redox-silent nanocarrier and a magnetically steerable “co-antibiotic” capable of re-sensitizing both Gram-negative and Gram-positive persisters to aminoglycosides and amphenicols without eliciting intrinsic cytotoxicity. The modular surface chemistry is immediately adaptable to other antibiotic classes or synergistic drug pairs, while the built-in magnetic switch offers an inherent safety mechanism to limit renal exposure. Remaining hurdles include lowering copper leaching (currently 0.15 ppm) below WHO drinking-water guidelines and tempering the early burst component to avoid nephrotoxicity thresholds; furthermore, implantable micromagnet or rotating-field designs will be required to extend magnetic guidance beyond superficial anatomical sites. Nonetheless, the collective data position CuFe₂O₄ nanovectors as a clinically translatable and environmentally retrievable platform for precision antibacterial chemotherapy, offering a tangible route to curtail the global burden of multidrug-resistant infections while conserving the therapeutic lifespan of legacy antibiotics.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.