Chonglei Zhang

Experimental approach to the microscopic phase-sensitive surface plasmon resonance biosensor

We designed and proposed a microscopic configuration of wide-dynamic-range phase-sensitive surface plasmon resonance biosensor based on differential interferometry between focused radially polarized and azimuthally polarized cylindrical vector beams recently (R. Wang et al., Opt. Lett. 37, 2091 (2012)). In this Letter, we follow the simulation results up with experimental verifications with a sensitivity of 7.385 × 10−7refractive index unit (RIU)/0.1°. It is also verified that the dynamic range of this system could be as large as 0.35 RIU in principle, which is only confined by numerical aperture of the microscopic objective lens.

Focused cylindrical vector beam assisted microscopic pSPR biosensor with an ultra wide dynamic range

A novel phase-sensitive surface plasmon resonance (pSPR) biosensor based on differential phase measurement between two cylindrical vector beams, namely radially polarized and azmuthally polarized beams, is proposed and studied in an inverted microscope. Different from a fixed angle or a relatively small angular range for SPR excitation in the attenuated total reflection (ATR) configuration, the signal beam focused by a total internal reflection fluorescence microscopic objective contains the entire angular range from 0 to the maximum angle given by the numerical aperture, leading to a dynamic range of 0.41 RIU which is over seven times wider than the best result of the ATR pSPR sensor. Moreover, with the technique of differential phase measurement between radial and azimuthal polarizations employed in our configuration, high sensitivity of ±9.05×10(-8) refractive index unit/1 deg can simultaneously be achieved in principle. The proposed technique maintains the unique advantages in terms of securing high imaging resolution and sensitivity with an ultra-wide dynamic range simultaneously.

Perfect optical vortex enhanced surface plasmon excitation for plasmonic structured illumination microscopy imaging

We propose an all-optical technique for plasmonic structured illumination microscopy (PSIM) with perfect optical vortex (POV). POV can improve the efficiency of the excitation of surface plasma and reduce the background noise of the excited fluorescence. The plasmonic standing wave patterns are excited by POV with fractional topological charges for accurate phase shift of {−2π/3, 0, and 2π/3}. The imaging resolution of less than 200 nm was produced. This PSIM technique is expected to be used as a wide field, super resolution imaging technique in dynamic biological imaging.

Sub-100nm resolution PSIM by utilizing modified optical vortices with fractional topological charges for precise phase shifting

We demonstrate an all-optical plasmonic structured illumination microscopy (PSIM) technique. A set of plasmonic standing-wave patterns is excited by amplitude-modified optical vortices (OVs), which have fractional topological charges for precise phase shift of {-2π/3, 0, 2π/3}. A specially designed optical aperture is introduced to modify the OVs in order to improve the uniformity of interference patterns. The imaging results of fluorescent beads reveal a sub-100nm resolving capability in aqueous environment. This PSIM technique as a structure-free, wide-field and super-resolved imaging technique is of great potential for low-cost biological dynamic imaging applications.

Dynamic plasmonic beam shaping by vector beams with arbitrary locally linear polarization states

Vector beams, which have space-variant state of polarization (SOP) comparing with scalar beams with spatially homogeneous SOP, are used to manipulate surface plasmon polarizations (SPPs). We find that the excitation, orientation, and distribution of the focused SPPs excited in a high numerical aperture microscopic configuration highly depend on the space-variant polarization of the incident vector beam. When it comes to vector beam with axial symmetry, multi-foci of SPPs with the same size and uniform intensity can be obtained, and the number of foci is depending on the polarization order n. Those properties can be of great value in biological sensor and plasmonic tweezers applications.

Plasmonic petal-shaped beam for microscopic phase-sensitive SPR biosensor with ultrahigh sensitivity.

Differential phase measurement between radially polarized (RP) and azimuthally polarized (AP) beams is an important technique in microscopic surface plasmon resonance (SPR) biosensors as reported in our earlier works [Opt. Lett.37, 2091 (2012); Appl. Phys. Lett.102, 011114 (2013)]. However, such a technique suffers complex beam splitting, detection, and data processing procedures for RP and AP beams which may lower the accuracy of phase measurement. In this Letter, a novel plasmonic petal-shaped vector beam is proposed instead of RP and AP beams, greatly simplifying the sensor system and enabling single measurement in differential interferometry. Moreover, an improved ultrahigh sensitivity on the order of 10(-7) refractive index units (RIUs) is experimentally verified in the proposed system.

A label-free approach to kinetic analysis and high multiplex detection of targeted drugs with phase surface plasmon resonance imaging

Targeted drugs have been increasingly recognized as effective agents against cancers because of their specificity. Kinetic label-free analysis is an essential tool to evaluate the affinity and reaction rate constants of drugs associated with their targets. Surface plasmon resonance (SPR) biosensors with real-time detection capability have been widely used as such a tool. The phase-type SPR technique based on Mach–Zehnder configuration has a high sensitivity because the measurement noise can be significantly reduced. In this study, we combine this technique with SPR imaging (SPRi), forming a phase SPRi biosensor to achieve multiplex detection. This phase SPRi biosensor, which features a 10−5 RIU sensitivity and a 30 μm × 20 μm spatial resolution, is applied for the kinetic analysis of a typical targeted drug—cetuximab. After preliminary experiments to measure the antibody binding reaction on BSA, the affinity and reaction rate constants of cetuximab are evaluated for its target, namely the epidermal growth factor receptor. The measured equilibrium dissociation constant (KD) is 4.20 (±0.62) nM, and the measured dissociation constant (kd) is 1.76 (±0.34) × 10−3 S−1, which are both close to the values reported in literature.

Graphene-based ultrasonic detector for photoacoustic imaging

Taking advantage of optical absorption imaging contrast, photoacoustic imaging technology is able to map the volumetric distribution of the optical absorption properties within biological tissues. Unfortunately, traditional piezoceramics-based transducers used in most photoacoustic imaging setups have inadequate frequency response, resulting in both poor depth resolution and inaccurate quantification of the optical absorption information. Instead of the piezoelectric ultrasonic transducer, we develop a graphene-based optical sensor for detecting photoacoustic pressure. The refractive index in the coupling medium is modulated due to photoacoustic pressure perturbation, which creates the variation of the polarization-sensitive optical absorption property of the graphene. As a result, the photoacoustic detection is realized through recording the reflectance intensity difference of polarization light. The graphene-based detector process an estimated noise-equivalentpressure (NEP) sensitivity of ~ 550 Pa over 20-MHz bandwidth with a nearby linear pressure response from 11.0 kPa to 53.0 kPa. Further, a graphene-based photoacoustic microscopy is built, and non-invasively reveals the microvascular anatomy in mouse ears label-freely.

Sensitive Gap-Enhanced Raman Spectroscopy with a Perfect Radially Polarized Beam

Gap mode surface-enhanced Raman spectroscopy (SERS) enables high enhancement of Raman signal. However, the polarization of excitation light shows great influence on the excitation of gap mode and hence on the Raman enhancement. Here, we propose a nanoparticle-on-film gap mode SERS accompanying with a new type of excitation source called as perfect radially polarized (PRP) beam. The PRP beam possesses a ring-shaped beam pattern that can be tuned to match the surface plasmon resonance angle under a tight focusing condition, hence improving greatly the excitation efficiency of surface plasmon polaritons, and eventually the sensitivity of gap mode SERS. Such kind of enhanced-Raman system with a PRP beam has a great potential on the applications such as single molecule Raman detection.

Concentric Perfect Optical Vortex Beam Generated by a Digital Micromirrors Device

We propose a kind of perfect optical vortex beam (POV) generated via Fourier transformation of Bessel-Gauss (BG) beams through encoding of the amplitude of the optical field with binary amplitude digital micromirrors device. We call them concentric POVs which consist of several POVs and where every POV has the same center and independent characters, and we confirm the correct phase patterns of the concentric POVs with the method of Mach–Zehnder interference and self-interference. This special property could be considered as a potential of implement to increase the orbital angular momentum communication capacity vastly.