Plasmon-assisted mass sensing in a hybrid nanocrystal coupled to a nanomechanical resonator

Surface plasmons on nanoparticles provide numerous ways to alternate and manipulate light at nanoscale dimensions, which have the potential to perfect the novel electronic and optical devices. Here, we demonstrate that plasmon-assisted mass sensing can be achieved in a hybrid nanocrystal coupled to a nanomechanical resonator. Compared with the traditional mass measurements, we use an all-optical technique rather than electrical circuitry, which may avoid the heat effect, to realize an ultrasensitive mass detection. The plasmon-assisted mass measurement proposed here may eventually enable sensitive measurement applications such as on-chip detection and analysis as well as identification of compounds.

Figure 1

Schematic diagram of a hybrid MNP-QD complex embedded in the center of doubly clamped nanomechanical resonator. When applying two optical beams, one is strong pump beam, the other is weak probe beam, this coupled system can be used as plasmon-assisted mass spectrometry. The inset below shows the energy levels of quantum dot while dressing the plasmon field and the vibration of nanomechanical resonator.

Figure 2

(a) The probe absorption spectrum as a function of detuning ${\Delta }_{\text{pr}}$ for the case $\Omega {}^2=0.05$ (GHz)${}^2$ (corresponds to the pump intensity $I=36$ mW/cm${}^2$, ${\omega }_n=1.2$ GHz, ${\Delta }_{\text{pu}}=0$, ${\gamma }_n=4\times {10}^{-5}$ GHz, $\beta =0.06$, $m_n=5.3\times {10}^{-15}$ g, $a_0=2.5$ nm, and $R=16$ nm). (b) The amplification of the right peak and the left peak shown in (a). The blue and the red curves for ${\gamma }_n=4\times {10}^{-5}$ GHz and ${\gamma }_n=2\times {10}^{-5}$ GHz have significantly different spectral widths ($100$ and $50$ kHz). (c) The four plots are the new features shown in (a), which are identified by the corresponding transitions between the dressed states of exciton. The original two-level quantum dot can be described as the ground state and the first excited state. When dressing with the plasmon field and the vibration of NR, these two levels are split into four dressed states, which is depicted in part (1). The transitions of (2), (3), and (4) correspond to the left negative peak, the central part, and the right absorption peak shown in (a), respectively ($|n\rangle$ denotes the number states of the nanomechanical resonator).

Figure 3

The probe absorption spectrum with and without the MNP. The other parameters are the same as in Fig. 2a.

Figure 4

(a) The simplified process for weighing the mass of Escherichia coli strain CA46 plasmid pColG DNA with plasmon-assisted mass spectrometry. (b) The probe absorption spectrum while landing the DNA molecule on the nanomechanical resonator. The blue and the red curves are the probe absorption spectrum without and with landing DNA molecule, respectively. The other parameters are the same as in Fig. 2a.

Figure 5

The direct proportional relationship between the accreted mass $m_d$ and the frequency shift $\Delta {\omega }_n$ for different masses of the nanomechanical resonator.